Unfortunately it is not true in general that the reason accounts are being banned is incivility. Censorship of unwanted opinions is very much real on this site.
Disagree completely, and I am far to the right of what I suspect the average hacker news member would be politically. Certainly opinions on the right get heavily downvoted, but that’s not censorship. Dang has corrected me a number of times for incivility, but he has never touched any of my posts because I happen to lean in the opposite direction of my colleagues here.
There is a flag in your profile called "showdead" that you can turn on to see the comments that have been deleted. There might be some minimum karma requirement for this, I'm not sure.
But I've had it on for a while now and I usually read a few of the dead comments. I see a lot of incivility, inanity, very little in the way of a politely expressed, well-thought out but unpopular opinion.
I didn't claim that incivility does not also exist. And the banned accounts don't show up in showdead anymore, either. What you consider "well-thought out but unpopular opinion" could also be subject to your personal biases.
Its possible that it happens, but from my admittedly limited anecdotal experience from seeing a half dozen or so people claim that they were banned for no reason and then taking a look at their comment history, they were absolutely banned for a reason.
Do you have an example of someone being banned simply because they shared an unpopular opinion?
Also "not true in general" implies that you seem to think that its a widespread problem and banning people simply for having an alternative opinion is one of the more common reasons people are banned. On HN that is something I find hard to believe.