Assume that other people have good intentions. Keep criticism constructive. Don’t attack people or insult what they post. If a reasonable person would think you’re being a jerk, that’s not okay. Persistent behavior that’s on the line is not okay.
In 1945, philosopher Karl Popper proposed the paradox of tolerance: if a society is tolerant without limit the ability to be tolerant is eventually destroyed by the intolerant. So, to maintain a tolerant society, the society must be intolerant of intolerance.