I think the point many of the more "patient" members here miss with negative feedback is that you are not doing it for your own feelings of reprisal or revenge but as a heads up to every other member who may consider trading with the bad trader.
Of course you can keep a personal list of 'blocked" traders to protect yourself but how does that help the rest of the community?
While you sit holding your little list congratulating yourself on your pristine morals through not leaving negative feedback on some poor surely well-meaning con-artist they can be firing off trades left and right to unsuspecting members who do not deserve to suffer because you want to withhold knowledge of a fraudulent person's actions.
If you have a bad trade experience, leave negative feedback. If, as in this case they choose to post "revenge" feedback then,as mentioned in this thread, there is the option to explain that feedback now. Even better if you can link to a thread like this or say examples of where the member has for example left other revenge feedbacks.
Personally I know I check these things before dealing with anyone here.