I agree, the pseudo-anonymity of the internet allows us to more freely criticize each other, but is that necessarily a bad thing? We can't improve without feedback, and negative feedback is useful too.
So yes, be more mindful that there's a person behind whatever you're responding to, and try to be polite, but at the same time don't hold back your opinions because you're afraid you might hurt someone's feelings.
It's really the politeness that is key. It's the difference between "You suck" and "Your X could be improved by Y" Sadly the tubes are clogged with the former and the latter is much less common. I wonder how many of us really remember learning to program and all the "stupid" questions we asked. Or installing that "Linux thing" the first time, or whatever. As we get farther away from that point it can be harder to remember just what it was like.
So yes, be more mindful that there's a person behind whatever you're responding to, and try to be polite, but at the same time don't hold back your opinions because you're afraid you might hurt someone's feelings.