Well having a discussion in comments can be productive if you’re learning new things. And there is a lot of good content here that many of us wouldn’t discover otherwise.
I imagine reading research or news posts on HN and commenting can be more productive than, say, reading reddit’s r/pics and commenting.
I’m sitting here commenting on someone else’s opinion on the internet, when I have far more productive things I could be doing.
Later on I’ll probably be narcissistic enough to check whether this comment got any upvotes.