I agree with you, I'm just saying that the reality is that people will have worse opinions of you / treat you worse if you have political opinions they consider unsavory. So practically speaking, if you are interested in your career, you shouldn't voice any controversial (given your employer) political opinions on public social media.

I don't want to give HR any more reasons to mistrust me: say I supported candidate X, and HR think's X and their supporters are racist/misogynist/anti-immigrant. Now if someone raises a complaint about me, legitimate or not, and HR sees that, they're more likely to assume I'm guilty. And at the end of the day, all else being equal (and it often is with HR because they aren't really able to evaluate technical work well), who gets the promotion: the person HR sees as edgy, controversial, and potentially an asshole because of their political views, or the person who doesn't share their political views?

Things shouldn't be this way, but they are.