I think that the idea in principle and on paper has some merit however. Even without the obvious cons to this idea the big one I see is the PLETHORA of posts about:
'We have undead available to Moderates! Why can't I roll up my Psi or Crusader as a moderate? That's garbage!'
Honestly, Q-races/classes even at their most basic are given enough bonuses/cons that it all evens out in the end. And the whole disintegrating corpse thing would just give you a PK shield, which is pretty OP IMO. Especially when there is an entire cabal dedicated to fighting undead, and it is lacking in members at least for the short while I've been around, having your RP be centric around eradicating undeads, and not being able to kill the blue undead running around because you already dropped him would be pretty unfair IMO.
Also dumb question if a moderate comes after your standard, you kill him, can he come back for your standard and be immune to you? Makes no sense that would be the case but if it is....
Moderate returning post death for a standard has no PK shield. Trust me. What he does have is the advantage of being fully dressed and back in your cabal guards face with the quickness.
I wouldn't mind seeing them open to Moderates. All it would do is gimp the qclass/race more than it would anyone who believes it gimps the Ruthless path. From what I've seen, people just don't want to be able to kill a Moderate to only be able to take two things off their corpse. Chances are, if you killed them once, you can easily kill them again after a while. If they initiate combat with you again that shield is gone and you can kill them again.
As far as that Cabal who is strictly after the Qraces, I find that whole Cabal kind of a oxymoron of sorts. It only allows Neutrals from what I've seen who are supposed to RP and have a reason to PK others which it does. But a majority of Qraces they are there to kill are evil and rarely are there ever Avatars for them to go after. Doesn't that pretty much make them a bunch of Goods in a Neutral protection? Which technically would get you an Outcast. As for Tribunal, yeah there are Goods in it, but most anytime I've seen them they have a majority evils too. But I have a beef with them, even when I was in the Cabal. 
I don't think you should fault the neutrals for the rarity of avatars. I'm certain that those neutrals also attack said avatars. They wouldn't be branded evil for doing so either.
A guy is in a convenience store buying beer when a man in a mask comes in with a weapon and points it at the clerk. The guy buying beer approaches silently and disarms and beats the crap out of the masked man. He then proceeds to buy the beer.
Does that make him "good"? No, he just wanted to buy his beer, and the only way he could do that was taking care of the obstacle. It wasn't a moral obligation, or a desire to save the clerk from harm, it was resolving an issue that was preventing him from making progress towards his goal.
You're looking at things strictly from the PK standpoint of killing an evil, and neglecting the fact that they are characters. They have thoughts, motives, desires and goals of their own. Who they decide to kill is greatly reflected by that, but the same is not always true vice-versa.
EDIT: Certainly not me, Brehan. 
Who said there isn't any Avatars around??
I didn't say there wasn't any, but there is however far more evil Qraces that one Cabal goes after compared to Avatars if there are any at all.
As for the above mentioned scenario, he's neither evil nor good, but he's not neutral either. More than likely he did it for himself so just in case the situation became bad, he didn't want to go to trial to point out a murder suspect and so on and so forth. So instead of doing that, he blackjacked that mofo and resolved the issue then and there.
If you can come up with another situation, we'll see if I can't bat that one away too. Other than that though, I know there are two sects to that Cabal, one of which is purely focused on Tribunal and the other focused on the unnatural both of which get skills/spells focused towards one or the other. Maybe we should start considering Crusaders forces of unnatural power because they use unnatural sources of power. That would give them plenty of options since there's like 400 of them running around and same with Undead/Demon/Vampires.
You didn't actually give any reason for that guy to not be a nuetral. He had no moral obligation one way or another. That's an act of neutrality. He's not doing it for the sake of the clerk or store, nor is he doing it to punish the would-be thief. At the same time, he isn't doing it out of a desire to inflict pain, nor his he trying to cash in on the sucess of the would-be thief (and therefore make off with the money). He's just trying to buy his beer and go home. That's neutral.
In the sense of the cabal, it is unified by a universal theme of nature. If it's unnatural, they don't like it. Can't blame them if a majority of their enemies are evil.
Haven't played a Crusader, so I have no opinion there. I do agree that there is a severe unbalance in qstuff that gives a tendency for said cabal to attack evils. However, they aren't being attacked because they're evil. They're being attacked because they are enemies.
How would you know if said people are your enemies? You wouldn't unless directly affected by them in some way. As a Neutral you're supposed to uphold balance between Good and Evil and when you simply just say, "Sorry but you're a Demon and even though there are 14 other Goods online and there's just you on that, you're my enemy, just saying." That isn't a good RP reason in my book whether you're in that Cabal or not. Not only is that Demon going to have all of those Goods on his ***, he just had a Neutral tell him he's going to try and kill him and unless that Demon is VERY good at PK, he's probably going to get jumped on all ends.
That guy can't be Neutral because for all you know he goes home and butchers children in his basement, or maybe he's a fellow follower of Purity. You never set any strict basis for it. Judging by that one situation, he's still a Ninja or a Thief who just blackjacked/strangled the guy to get his beer and leave. If by the basis you say he's doing it out of neutrality because he's not doing it for the clerk or the store or to punish the thief, that leads me to believe he's a follower of Greed because he's doing it for himself more than anything.
Now lets say that if IG the Watchers saw character A beating the crap out of everything in the forest that wasn't harming it but was rather protecting it to save it, whilst leaving the Fire Giant Loggers alone to cut it down and then when they were finally able to harm them, so said Watcher kills character A, that would be justified as they themselves are unnatural and thus deforesting nature and killing it off. Now if Watcher sees Character B who he's never seen before and he just so happens to be a Lich but he's killing off a bunch of other unnatural beings (leveling or just a distraction) and the Watcher kills the Lich without a word other than the person is a Lich, I find it very hard to believe that's a Neutral RP whether that's the Cabal or not.
So my stance still stands, as the mugger situation can happen every day, where as it doesn't show signs of his alignment of any which way. I as a person find myself a Neutral Neutral because although I am a nice person IRL, that doesn't mean I'm Good. I don't go out of my way to help people unless I know I can do it without harming myself (neutral mentality), I don't go out of my way to make people's lives a living hell (neutral mentality) and if it came right down to it if I had to kill someone to save my own life in self defense I'd do it (again neutral mentality).
Granted in this game we don't have the obligation to show our back story to everyone we encounter because we'd be explaining ourselves for a LONG time. However, I've seen more Watchers take advantage of those Qraces whom are already low on health from having fought someone or something recently to their advantage which to me is clearly an Evil thing to do. Now if they were to kill said people and never full loot or loot at all that would be another story but back in my day that was rarely ever the exception.
I've never played a Crusader myself, but there are things they do that I would lean towards putting them on the unnatural selection list as well. Some people would probably argue that point, but that's another matter entirely.
The roleplay involved with that section of Watcher dictates that they kill the unnatural. Good or evil, it does not matter.
If you're a demon, and there are 14 goods on and a neutral sworn to kill the unnatural, it sucks to be you. The RP of the cabal, however mandates that said neutral needs to destroy you. It doesn't make them a "good under neutral protection" as you claim it does. It makes them neutral with an evil enemy. Again, we come back to this: You cannot fault the neutral for the rarity of unnatural goods. Just because the nuetral kills demons and undead, does not mean he is a good.
If the guy buying beer did any of those things, I would have put that in... that's the equivalent of saying "That neutral might be RPing his cabal properly, but I bet he's not a neutral when not in a cabal!"
As for those watchers killing those weakened... that's not really EVIL, just really, really low. The RP of it is still "That is an enemy of my cabal. It is my objective to kill them." You're assuming that the character is evil because it took advantage of a weakened enemy. However, that act isn't truly an evil act. Hell, even goods can do that, provided said enemy is evil. So, again, not an act of evil to do so. Yeah, it sucks. I know the pains of dying to an enemy that caught me immediately after another fight. But... c'est le vie. Nobody said qraces/qclasses were easy.
Neutrals are not supposed to uphold a balance between evils and goods in any way.
Neutrals need a solid reason to kill someone, no matter their align.
Anything unnatural falls under that category for a Watcher, more so, but not only, for a Stalker.
If you kill someone already weakened from someone else or not is a matter of playstyle and not align. Someone who tags ALL the time won't get high up in any cabal.
Actually I recall sometime in the past that a Neutral doing that to a weakened enemy would be considered an evil act, where as if an evil does it to another, well they're evil so they get away with it. I don't know if the Neutral would be OUTCAST because they took advantage of it too many times, but perhaps once or twice would be understanding since it could be completely accidental. The RP of the Cabal doesn't mandate it, it's a certain sub-Cabal that does, the other is bent on destroying the Law. Granted they are allowed to do both and that's what I gather from the help file and what I did with my own at the time.
As for a 14 Good and 1 Watcher I'd hope you'd coordinate the attacks so it's not a 15 on 1 gang bang because I'd feel sorry watching them run a train on that.