I too couldn't care less about what two consenting adults get up to though I'll judge them if they don't take very strict measures to prevent accidental pregnancy. Others may judge me for that opinion, but freedom of speech also implies others' freedom of speech to voice their concern with you.
I also think the American sensibilities regarding potentially harmful words or behaviour are stupid, part of my set of "those silly Americans" opinions. Those "this person tweeted some bad joke ten years ago" headlines are depressingly stupid. Luckily, I haven't encountered any such behaviour over here unless it's about celebrities.
If you think your opinion might cost you your job, a) that says a lot about your immediate environment/work culture and b) you can get around that by expressing your opinions under an account that's not directly linked to your name or work. Your opinions about controversial topics and your github username shouldn't be too closely connected if someone malicious might try to use your opinion against you.
Another thing to consider is when to voice your opinion. If someone asks "what do you think about incest" then sure, you should be able to voice your opinion without issue. Sometimes, though, it's best to avoid controversial topics when discussing other topics, even though the two are tangentially related.
I've put up plenty of controversial opinions and I just accept the negative internet points. I've never had crazies go after me other than two or three people pissed off at my opinion that decided to down vote all my post in a thread, which is too sad for me to care about.
Make no mistake, though, the HN hive mind is very much a thing and when you hit certain topics (specific ways of doing business, for example) you can find reasonable posts that go against the flow all the way at the bottom in light grey. You may need to enable showdead to see them (they're not always down voted either, sometimes it's just spam detection making a mistake).
One thing to consider, though, and something I've had to do over time, was to consider the basis of some of your opinions if you find yourself getting down voted across the board. Downvoted comments with no responses are often useless, but when people start stating their reasons then it may be worth to consider them. Everyone else can be wrong, especially inside echo chambers like social media, but it's still worth it to challenge your own position every now and then.