To me, the fact that HN is one of the few remaining community-driven sites worth reading is proof enough that its system of downvoting and flagging works very well.
Other sites with similar, though less rigid moderation systems have fallen deep. Slashdot is a good example. I know it since it was founded and it used to be great. But starting from 2012 or so it went into a downwards spiral. For a while, during the US election cycle, it was almost completely overtaken by bots and trolls, and even though they've been fighting hard to improve the signal-to-noise ratio by tweaking their moderation assignment algorithms, it is barely worth visiting nowadays.
I'd rather let my ego be hurt a little bit by being unfairly downvoted from time to time than having to deal with hundreds of opinion posts. People tend to overestimate the value of their opinions, and the vast majority opinion posts are redundant anyway. I like HN because it keeps political discussions away and focuses more on informative content and discussions among adults than on opinions.
There are also certain topics that simply seem to be impossible to discuss on the Internet. Frankly speaking, in the 25 years or so I'm on the Internet, I cannot remember a single meaningful or insightful discussion of US politics, hate speech, religious faith vs. science, gun laws, abortion, and climate change. I've also never experienced a good discussion of political positions in general on the Internet and also have no desire to participate in such discussions. Maybe there was some information, some useful link to statistics or literature here and there, but overall the quality of the discussion of such topics is abysmal. If it's already hard to have fruitful conversation about an issue face to face, then the topic for sure will not work on the Internet, and I can gladly do without these discussions on social media sites.