The parent post made an assertion, but did not really justify that assertion. Sure, it's easy to say that in some abstract sense "down votes don't matter". I believe that myself, in that sort of abstract / hand-wavy sense. But real life experience shows us that down votes do matter to people - at least some people, some times, in some situations. Why? I'm not a psychologist, so I'm not going to pretend to understand the deeper aspects of that. But it seems self evident to me that it's related to the other evolved responses we humans have, related to peer approval, social status, recognition, embarrassment, etc.

But _why_ does it feel kind of grating? Why does it frustate you?

In the specific case I mentioned, I think it's largely about the mismatch between expectations and perceived subjective sense of "right/wrong" and reality. I expect random throwaway comments that just say "taxation is theft" to get downvoted. But when I spend 30 minutes doing research, looking up citations, and crafting a carefully composed response to something, to try to make a point or provide a useful reference to help somebody and then that gets down voted, it triggers that instinctive "unfairness reaction" that we have. Or that's my approximate theory anyway.

Moreover, why do you only care about the downvotes?

I think because a downvote is a form of disapproval, and it's done in public, and it correlates to our desire to avoid being shamed / embarrassed, especially in front of others.