This sort of conflict has happened before. IIRC it was decided in previous cases that if you receive negative ratings for no good reason, then it's OK (but perhaps sub-optimal/petty) to send retaliatory negative ratings until the first person removes their ratings.
I would draw similarities between someone leaving negative trust in retaliation of receiving a negative rating and someone leaving negative trust because someone was speaking out against them via posting. I think it is pretty well established that when someone leaves a negative rating when they are spoken out against, that they do not have a place on the default trust list. I can provide a few examples of people getting removed from default trust after leaving negative ratings for these kinds of reasons, however I am fairly certain that you are familiar with them already.
If someone leaves a negative rating for no good reason, then they should be removed from default trust (if they are on it) and their trust ratings should be ignored by others. I would argue that someone leaving a negative rating does not make them a scammer (unless they ask for something of value in return for removing it, in which case they would be an extortionist - however I don't believe this to be the case in this situation).
I think this is almost exactly the same as what happened when TBZ was previously removed from Default Trust, except the person in question has made a post about TBZ, while the person in question in this situation left a negative rating - the only real difference is what medium was used (posting verses trust).
It's not a good idea IMO, but Luke's "blacklist" is intended to stop only certain types of spam, not to blacklist any specific people/companies. The companies affected by this can easily bypass it by using Bitcoin properly. Even if Luke was trying to blacklist all gambling or whatever (which he's not), that still wouldn't be a good reason to give him negative feedback; it doesn't make him any more likely to scam someone.
I think this is open for debate, however some may argue that his "blacklist" was something that would have harmed Bitcoin and as a result his work should not be trusted.
Probably his BiPolarBob feedback should be reevaluated, though, especially after all this time.
Hi somewhat implied above that he is not going to do this.
Posting vs using retaliatory trust ratings are very different things and should be distinguished from each other. When one is posting in the forums, it is meant as a means of communication, and that needs to be protected. It is very easy for some one to simply claim some one is lying about them, or say something they said is untrue to try to justify harming their reputation in retaliation. This atmosphere will make sure no one ever speaks out about the abusive behavior of others and it will continue to grow unchecked. This is why in my opinion negative trust ratings should not be left for simply what people say, no matter how full of shit they are, as long as they otherwise follow the forum rules and are posting in the correct area to make the complaint. In the past there was no neutral option, so this also helped to condition people to jump right to using negative ratings, and this should stop since we have another option now.
Now as far as leaving retaliatory ratings (negative ratings left after another user left one first), I think this should be protected, even for those on the default trust, and I will tell you why. People use the reputation system as a tool here to exploit honest people into submitting to them. They spend the energy and effort building up a trustworthy reputation in an environment completely saturated with fraud, clawing out a name for themselves, then they have something to lose that can be used against them to make them either ignore abuse from others, or become complicit in it. Additionally, some people try to say that anyone who leaves retaliatory ratings is abusing the trust system, but I ask you this simple question... do you think if people know for a fact you will not retaliate with a negative rating in kind, would that not give them even more incentive to abuse the trust system to begin with knowing it will cost them nothing?
It would be analogous to saying in public that you are so against violence, that you wouldn't hit some one back even if they hit you. If some one knows you will not retaliate, and they have a reason to dislike what you say (for reasons that may or may not be valid), they will be more likely to hit you. Furthermore what is to stop a single person from using lots of accounts with reputation to do this further amplifying the problem? Retaliatory ratings should be allowed, but only if the other party did so first, and not just because of what they post. Neutral ratings are perfectly sufficient to deal with slander in threads.
In summary the difference is the forum is supposed to be for communication (even if you consider it bullshit), and the trust system should be for building a trade reputation, identifying untrustworthy individuals, and defending the reputation of ones self and other reputable individuals so we can all enjoy the benefits of an effective trust system filled with reliable information, not just bickering, which is what belongs in the forum is anywhere.