Granted, the title of that question – Would Trump's “mafia don” defence work in court? – could be perceived as inflammatory or defamatory. But it is not actually defamatory: it is hyperbole or "rhetorical flair" that, given the substance of the question, I think makes it a great title, and one that is consistent with Stack Exchange standards and practices.
The question itself is arguably good, and it is written in a way that invites good answers. It begins with a very public scenario and then relates that to a more extreme and abstract hypothetical that produces an on-topic question. (Without that abstraction the question could be seen as soliciting prognostications on a real-world trial, which would be off-topic.)
The problem, as illustrated by the question here, is that the public scenario involving the U.S. President has been highly politicized, and the author of the question in question did not take pains to avoid triggering partisans to that public spectacle. But the author did not accuse the President of incitement: Congress did.
The author of that question gave a reasonably objective summary of the accusations levied by Congress, and then related that summary to a more salient hypothetical involving a "mafia don." The analogy is illustrative, not gratuitous. I don't see the analogy as lunatic. If the analogy is flawed or logically inappropriate, that can be dealt with in answers.
I should point out that I'm a moderator, and in that capacity my goal is to keep things here running smoothly and in-line with the community rules and guidelines. The Meta question here is fair: the asker argued that that post crossed the line of civility we strive to maintain. My answer here explains that I don't see that post as a violation. (But I'm only one of the moderators – any of the others can choose to weigh in or disagree and step in to take some action on the post.)
Now, as a moderator I don't exactly have the last word on this: As of this moment three users with sufficient rep have voted to close that question. Two more and it will be closed. Furthermore, if it draws enough negative attention that it becomes unduly disruptive one of us moderators may step in and take some measures to moderate it – even if we don't personally think it has crossed a line. But we do try to be moderate in our moderation ;)