I think that the culture of a given forum plays a huge role.

There are some places where commenting is meaningful because you're a part of some closely-knit, stable community, and you can actually make a dent - actually influence people who matter to you. I know that we geeks are supposed to hate Facebook, but local neighborhood / hobby groups on FB are actually a good example of that.

There are places where it can be meaningful because you're helping others, even if they're complete strangers. This is Stack Exchange, small hobby subreddits, etc - although these communities sometimes devolve into hazing and gatekeeping, at which point, it's just putting others down to feel better about oneself.

But then, there are communities where you comment... just to comment. To scream into the void about politics or whatever. And it's easy to get totally hooked on that, but it accomplishes nothing in the long haul.

HN is an interesting mix of all this. A local group to some, a nerd interest forum for others, and a gatekeeping / venting venue for a minority.