I think the question is a bit muddled by the example, honestly. This was someone lashing out and being hateful, regardless of what their particular political leanings were -- and it seems like the hatefulness is more off-putting for most folks than the politics.
So if you were to ask, "is it bad to speak hatefully outside of your comic, and should you keep that sort of behaviour out of your online presence?" then my answer would be an unequivocal yes!
But, "should you keep politics separate from your art" is a more difficult question, because I don't think it has to be inherently alienating or hateful to speak on your experiences. As a person with a small following, I want to be authentic but also thoughtful. Sometimes that means I do talk about my feelings on things that are happening to me and the people around me in the world, and sometimes that means I think it over and decide that what I have to say is better vented about with a single friend in private messages. I think the answer of where that line's at is going to be different for everyone, because what's most authentic for you is going to be different for everyone.
I have run across artists that I unfollowed because the things they were passionate about were stressful for me -- but like, that could be true of anything, right? Draw tons of pictures of dragons, and you'll attract people who like dragons and lose folks who are sick of dragons, and maybe get some of your followers interested in dragons when they weren't before. Talk a lot about your experiences in feminism, and you'll attract folks who care about that topic and lose folks who are sick of it, and maybe get some of your followers interested in feminism when they weren't before. There's a lot to be gained by being kind, thoughtful, tactful, thinking before you speak, and not feeling the need to jump into every argument or weigh in on every issue. But there's also a lot to be gained by finding a way to be thoughtful and kind and still be your honest self.