> "Isn't it enough that downvoted comments become gray?"
Nope. That doesn't show you the difference between a barely-passable comment and an excellent one.
I learned a lot during my early HN days, when comment scores were visible, simply by looking at what sort of comments tended to score 5 points vs 1 point, or 15 points vs 5 points, or 40 points vs 15 points. Here on HN, "just post short memes" tends to be met with negative signals; thoughtful, helpful, and accurate responses are met with positive signals. I found it helped to be able to see that, and I think many newer HN commenters have the same misconception as you do because they haven't had that same training.