How do you handle unethical behavior?

In a really good episode of Star Trek Voyager, the holo doctor (who never gets an actual name) is confronted by a rather difficult choice. To save the life of a crew member he has to use the research made by a man who acquired his results through unethical ways, by experimenting on unwilling patients. The doctor reasons that if he decides to use those research results, that would be like justifying the means in which they were acquired, and decides that he has to find another way.

The question here is; would it be ok to use something which has been acquired in unethical ways, even if it's for something "good" (definable of course)?

First of all I'd like to say that I don't agree with the Doctor in this episode. I don't think that using unethically acquired research in anyway has to justify the means in which they were acquired. I usually apply a simple "what would I want" to any moral questions, and I would of course not want to be part of any freak experiment against my will. But if the harm was already done, I think I would prefer the results to be used to save lives rather than be discarded. This doesn't mean that getting the research in this way was ok in any way. Besides, how much of our knowledge today doesn't origin in research which has been acquired in what we'd today consider rather unethical? We improve, not by discarding our mistakes, but by learning from them and finding new ways to get understanding about things.

So anyway, now that I've made that clear I'd like to make a further point. This kind of dilemma can be found in a game like WoW too. People behave unethically all the time (unethical as in alot of people don't agree that it is a good behavior) which I have mentioned in some posts before. I can think of two good examples and I'd like to ask you what you'd do to handle them, if at all.

The Battered Hilt
It has become something of a standing joke in trade chat of my server (and surely of other servers too) to sell a "Ninja'd Battered Hilt". Although many of them probably aren't ninja'd at all, I am sure alot of them are. And if someone admits to having ninja'd it, aka stolen it from the rest of the people who also rightfully should have had a chance to it or needed it more, would you have any second thoughts as to buying, it at all?

I will go against what I just say here and say that it is wrong. In doing this, you might not justify the behavior, but you'd definitely encourage it. People see that they can actually sell their ninja'd item, which is the very reason they ninja'd it in the first place. Kinda like stolen art. If you buy stolen items, you encourage the whole idea of stealing items to profit from them. But you want the Battered Hilt of course and the ninjaing has already been done, so would it be so wrong? The difference to the example with unethical research in the "real world" is that us players have very little power against taking action towards players who steal items, whereas I hope that governments around the world have more power to prevent unethical research from taking place (but maybe I am naïve). WoW is based on such a big part on mutual trust and the will for everyone to be kind to everyone else, that there isn't much we can do but govern our own actions. Only the GM's has the final say.

The NINJA guild
It is similar to my previous example, but on a bigger scale. On my server, and again probably on several others, we have an official ninja-guild. A guild whose members openly admit to being ninjas when pugging with other people. Maybe you would avoid any pug raid in which one of these guild members happen to be the Master Looter (which I do), but would you go to any further lengths to "punish" this unethical behavior? The problem is that you would have to punish every member of the guild, even those that have never ninja'd anything, since you wouldn't know the ninjas from the non-ninjas really. On the other hand, those people agree to share their guild tag with commonly known ninjas without doing anything about it and maybe they deserve a little taste of the "collective punishment" as we say in swedish?
Would you for instance turn them down if you pull your own pug group together? Say "sorry, I don't invite ninjas". Would you be arsed? And if you really needed that healer and the only one you get is one from this guild, would you still stick with your policy or bend it some this once out of convenience?

Again, our only way to affect other people in a game like WoW is by making clear that we don't accept that kind of behavior. We can't throw them into jail (ban their accounts) or take what they stole away from them, so the only way we can hope to change that behavior by setting our foot down and say "we don't want anything to do with people like you" (and ticket a GM and hope for something to happen). That is, if we can be arsed.

The problem with any system that allows players to report unethical behavior is that it can, and will, be abused. A game like WoW is somewhat similiar to real life in this way too. We have to go to the "police" (GM's) when we have an issue and then wait for their bureaucracy to take its time before something might happen. Like I mentioned in my post about ninjas, Blizzard doesn't think it's big enough of a problem to put man power enough into it to make sure people stop doing it. And unethical behavior overall really isn't much of a problem, yet. But when people get away with it so easily, they won't be able to stop themselves from doing it (or so it seems anyway). And maybe that means we need a little social courage to step in.