The best description I've heard of twitter is that it's a mirror disguised as a window. Twitter can be great for getting a diverse perspective that most people wouldn't otherwise have access to. It can also turn into an echo chamber that only reinforces and amplifies your existing biases. If what you see on twitter is hate, vitriol, and groupthink then maybe what's ugly is you, not the world you think you're observing.

I am not sure what good banning people from the service does. I don't think it stops people from thinking outrageous and hurtful things. It just moves them elsewhere and makes them less likely to encounter people who could help them be more civil and less sensational.