This makes so little sense. Why would I care about signalling my 'virtue' to a bunch of anonymous people who have no idea who I am? I can say something nice or harsh because I believe it was affect the people who read it, even though I'll never meet them. That is rational even if it doesn't benefit me, if I care about the experiences of other people. But acting a certain way to gain positive regard for an anonymous identity is dumb af.

And the main reason I or anyone else acts compassionately online is probably just that it's the first and easiest reaction. I don't troll or harass people, even if I would suffer no consequences from it, simply because I have no interest in doing so. I say something nice because that's what I want to say, it's not an effort or a cost.