I mean, yeah. This isn't true of everyone. But for a large portion of people, getting downvoted feels bad. Maybe the "proper" view of karma should be "the karma I receive is merely an indicator of how valuable/accurate the comment is, and I should adjust my view of that comment accordingly." But just because something is irrational doesn't mean I can change it, or that the effects aren't real. And this is fairly common, from what I can see.

As for the "valid expression" thing: It gives too much power to a single individual over the type of content that is here. From what I and some other victims of downvoting can tell, it is the action of a single, well-known user who has decided to downvote people who express a certain view. I am fairly confident (>80%) that at least a few people have been driven off this site from mass downvoting.

What this means is, one person can affect who is on the site in a somewhat substantial way, even if the community does not agree that this is a bad view.

(If you want, you can PM me for more details.)