Another big difference is that I'm not advocating for us to "repeat" that we should all be positive. It's not about public proclamation – it's about addressing individuals and their individual acts. That's what the communal discourse is made up of. Like you're saying, simply shouting "let's be nice" obviously doesn't work.
I'll add another thing to my list of suggestions: be really deliberate about educating people on the principle of charity. Instead of assuming that the other person is dumb/shortsighted/etc., assume that you're not giving their thinking enough credit.
> that's orthogonal to the inevitable formation of other communities
So what? Drive the downers out of JS-land, or whatever community you care about. You had been saying that even that shouldn't be bothered with. But if it can be accomplished, who cares if they all go off to learn Brainfuck, if that's the only community that will accept their behavior?