My view is that I take some trouble to try and be polite, if I have something to say that disagrees with another poster. However, there is next to no-one here that I actually know personally, and I hope that no-one would take any of my comments personally, i.e. I am not criticising them, just offering an alternative viewpoint. I think that it's possible to disagree with someone's post without making it personal.
Also, if anything I say provokes someone's criticism, well, that person doesn't know me, and even if it sounds a bit abusive, well, I don't have to take it personally.
Having said that, it's perhaps a good idea not to just fire off if you want to criticise, but to re-read before the final click, to check that the tone doesn't come over as too offensive.