Lawyers are disbarred either for violating their professional duties or for committing felonies.

I don't see how that would work. A patent troll's actions are generally perfectly legal; they're exploiting structural weaknesses in the patent system (low cost of getting a patent) and legal system (high cost of defending against a patent lawsuit).

In principle, their professional duties could in some way preclude trolling. In practice, we'd have to get a bunch of lawyers to agree to pass on a crapton of money. But still, it may or may not be easier than getting politicians to pass on a crapton of donations to get the laws themselves changed...