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.
First, I think it can be both, and second, it's important to be careful around the common fallacious defense for shitty people where the implication is that they should not be judged or experience certain ramifications (legal or social) because "it's all just trolling", "for the luls", "you can't take what he/she says seriously", "it's your fault for getting offended", etc. There are certainly arguments to be made one way or the other in these cases, but one standout damning feature that's common to a lot of them (including this one) is that of public reception. If you encourage something, all that matters is how likely and severe the consequences of that are, regardless of whether you were "just trolling". If you're a famous and wealthy person with a cult of personality and a politically divided following (or even if you just hit a couple of those notes), it's your responsibility to not offer people thousands of dollars to get hair from your enemies, even under the (conveniently subjective) guise of sarcasm/joking.
I wouldn't disagree with the former interpretation, but publicly offering thousands of dollars for something carries a real risk somebody will take you up on the offer.
It's strange because I think if the same $5000/hair offering were made for an average person it would be much more serious. But in my mind someone who is so prominent and guarded by the Secret Service is in virtually no danger from such an outlandish thing. But I do understand how someone would see it the other way and not be comfortable with the risk at all.
I think there are people whose jobs are to determine the appropriate punishment for criminal actions. They might be able to give you a tighter upper bound
Your post was, "Never threaten a Clinton (I anticipate downvotes.. and they'll be reinforcing my position that they're off-limits)". Your position, AKA existing ideas, are "Never threaten a Clinton", and "they're off-limits", implying that they have special and unfair power/treatment in the political and legal world, but specifically with regards to the specific outcome of the specific case of Shkreli. The parent's criticism was in regards to your attitude on downvotes, which makes sense independent of whether your position is justified or true.