Tone is difficult to convey in written text, yet fundamental in spoken language. People generally tend to read any given sentence as much more aggressive than the author intends.
At the same time, we live in an environment where almost any discussion you have with another person, serious or otherwise, is governed first and foremost by the framework of there being a winner and a loser. And you don't wanna be a loser, do you? so you have to claw back to emerge victorious.
Most of the time people don't really have serious or consistent beliefs about anything in particular, but when discussing things will fall into a position and then try to defend it to "win" and at that point it doesn't even matter if they know, care, or even agree with what they're saying. It's all about not getting owned.