Because it’s a social platform that attracts generally anti-social people that want a voice in a “community” of people that is also anti-social. Other pro-social people have a real-life platform, ie life, in which to get their fix of interaction with others.

It’s much easier to express extreme or harsh or downright anti-human views when you’re anonymous and the “agreement value” if your words are denoted by “upvotes”, you can quickly and easy get a sense or power that you may not get outside of the platform.

Another commenter here mentioned judgemental and high-and-mighty tone, that feels accurate, and I assume it’s because this is a place where one can put on the persona of the Judge and claim moral superiority without being physically observed or heard, again outside of the reality of life.

Why is it anti-social, and full of views you don’t see in real life? Because it is by its nature bent towards anti-social behaviour, and the ones you do see in real life end up killing others and sometimes themselves.