There's a pervasive idea in discourse of any kind that it's a fundamental rule of argument that you have to "respect your opponent's opinion". If you don't, you're as good as disqualified.
This idea is absurd. Why should you "respect" something you know is wrong and destructive? Should you "respect" the opinion of someone who claims black people are sub-human and should be slaves? How is advocating mass theft and violent mob rule and victim punishment any different? (Remember that everyone's actions have to be analyzed from their own perspective.)
Anger is not a fallacy. Even flaming is not a fallacy. Dismissing your opponent's argument for the way they express it is what is a fallacy.
It's really just a tool to stop good people from being listened to, because usually the people who don't "respect" opposing positions are the ones in the right (they have the most reason not to).
The tvtropes article on "the Hitler Card" (I won't link it) makes a claim to the effect of "it's generally agreed that whoever plays this card first loses, because having to compare your opponent to one of the worst mass-murdering tyrants in history means you've run out of better arguments". The fallacy here is crystal clear. A comparison is not invalid or a bad argument simply because it is extremely insulting. If the comparison is apt, if the person really is advocating something that is not meaningfully different from something they abhor, this is a perfectly sound argument.