Criticism
I generally respond to criticism by ignoring it. Two things.
First: it would be unrealistic to expect people care about me beyond the utility I offer them. I can expect politeness, almost by definition, since politeness can be defined as “the minimal courtesy due a stranger.” But I can’t expect anything beyond that. My employer cares about me insofar as I can turn them a profit. The waitress at a restaurant cares about me insofar as she can get a tip. I should not expect people to care about me beyond the utility I offer them. They care so long as I’m useful, and only that long.
Second: criticizing other people makes us feel good about ourselves. Pointing at someone and calling them a fool makes us feel better because we must be wise by comparison. Calling someone else a jerk makes us feel better because we must be nice by comparison. Calling someone awkward, or clueless, or morally reprehensible — all of these criticisms give us a boost. Criticizing someone else makes us feel good about ourselves. It follows that other people offer us utility when we can criticize them. And for a stranger, this is often the only utility they offer us.
Put those two together, and what do we have?
Well, to a stranger, I’m only useful because they can criticize me to feel better about themselves. I can’t expect them to care about me beyond that. That’s all I offer them. Thus, if I interact with a stranger, I can expect them to be a jerk because the only thing I’m good for, to them, is being a pincushion.
This, incidentally, is why politeness exists. The point of politeness is not to be “nice” per se, so much as to create an artificial distance so that we’re not constantly poking each other. And if you’ve ever wondered why people are such jerks online, this is also why. Politeness doesn’t apply online. Online, your potential “utility” outweighs politeness.
This whole answer is terribly cynical. I have a bit of myopia problem: I tend to apply an acid-wash of cynicism to everything and assume that whatever it eats away was not worth looking at in the first place. So let me walk it back a bit: this answer represents a “safe” outlook. It’ll keep you from getting burned. The perspective I’ve outlined here will save you a lot of grief. But it can also cause you to miss out on a lot of rewarding interactions on the assumption that everybody is just a self-interested jerk — an assumption that, in all honestly, simply isn’t true. The sensible middle ground is to adopt this perspective as a shield to shrug off the slings and arrows you’ll get, especially if you use the internet a lot, but be brave enough to let it down sometimes and connect with people. If not, you lose something very important.
Constructive criticism has value, but most criticism doesn't as it is either not constructive or betrays a lack of understanding as to what you have written/said. Pareto Principle comes into play here, which is why it is best to ignore most of it, otherwise you bog yourself down addressing it and lose focus.
I am less depressed now than I used to be, due to medication, therapy, better habits, having a more active social life, lucking out with a nicer boss in my new job, and earning more money. That said, I can still model depressed-me's mental reactions to things pretty well. So it's interesting to see the discrepancy between depressed-me and current-me in how they react to your two things. Depressed-me thinks they're self-evident and anyone who thinks otherwise is either kidding themselves or naive. Current-me thinks thing one is empirically repeatedly falsified by past experiences (although the ratio of falsification to overall experience count is more like <10% than >50%) and thing two just isn't me (current-me feels bad calling others fools unless it feels justified eg in retaliation to them calling me a fool, and feels rewarded by calling others good as long as it refers to concrete examples other praisers overlook). Depressed-me and current-me disagree on pretty much everything from emotional valence to predictions to recommended actions, but they do agree on your last paragraph's "safe outlook" moderated take.