That's true for political parties, for sure but if some Trump supporter jumps into a leftie thread and barfs "suck it byatches, your spook in chief is gone and your byatch is bleeding from her whateva" are said lefties under any obligation to hold back on those hurtful accusations of bigotry?
I'm tad surprised that I have to explain this, but okay. Obviously, meaningful discussion is a two way street. It does require the other party to be willing to argue in good faith, and therefore it excludes individuals like internet trolls. Unless you're arguing that every Trump supporter or indeed right winger in general is on the same level as an internet troll, I'm not too sure how this is relevant.
Also, I thought I was quite clear in that I'm not against accusing bigots of bigotry. Like I said, telling your opponent that they're wrong and explaining why they're wrong as thoroughly as you possibly can is an important part of a political discussion. This goes for bigotry as much as any other issue.
In any case Clinton went to great pains to talk about the Trump voters who weren't Deplorables but merely justifiably worried about their economic and social prospects. Fox News, Brietbart, Heat St et al filtered that into "SNOOTY McSNOOT CALLS Y'ALL DEPLORABLE!!!"
Yeah, that's also an important (though somewhat separate) concern.