I guess the main thing is that if you’re going to argue for something very unpopular, rather than arguing for the sake of your opponent as they are today, argue for the sake of uncommitted onlookers and for the sake of the opponent a week from now after they’ve had time to calm down and reprocess. Respond to their arguments, of course, but do it in a way that illustrates to less polarized people that you’ve got a point, rather than trying to convince your opponent or finding specific errors in the opponent’s reasoning/self-justification.
When an issue is as polarized as this, people very rarely switch sides publicly (unless they’re shilling and they didn’t hold the original position to begin with), but people can cringe from the side making bad arguments, quietly distancing themselves, and a few months or years later show up on a different side.
If you want that side to be your side, it’s nice to present a pipeline that does that. People who cringe from bottom-of-the-barrel leftist discourse can fall into alt-right pipelines, which you presumably don’t want, so ideally you would want to have examples of (leftist) influencers whose takes you find reasonable, ideally on the case itself. For example, LegalEagle (“it is plausible that the jury was right that murder under Wisconsin law was not proven beyond reasonable doubt”).
The hate is not really avoidable except by forgoing this venue or not arguing your point, but like with the hate thrown towards peaceful climate activists, it is not a sign that you’re doing a bad job.
The fact that Republicans wouldn’t do that doesn’t change the fact that there are undecided voters that would do that. If you think non-whites aren’t capable of being as conservative as republicans, you’re going to be disappointed time and time again.