I think "I anticipate downvotes" is fine. "If you downvote me I will lean harder into my position" is basically blackmail (admittedly lame and ineffective blackmail), which is why I downvoted it.
I'm a little more strict, and draw the line at pretty much any extraneous assertion that your audience is going to disagree with you. E.g. "Controversial opinion: ...", "The HN crowd will downvote me, but ...", etc. It's an unnecessary injection of negativity, pettily frames one's self as the underdog, and provokes by implying that the people you're addressing are wrong before they've even replied to you. Obviously the internet is largely not a place to give crowds the benefit of the doubt, but it's critical for places with a shred of the expectation of real discussion, like HN.