To be fair, the block button feature is not abused. When you understand that there are different treatments from Twitter Police Forces regarding what you can write (or not), you'll see why people block others.

If you are on the side of the establishment, you can do whatever you want, even threat people of murder. You can report those posts but they won't even investigate.

However, to those on the other side of the fence, it is the polar opposite. Even saying things which don't break the Twitter Policy in any way can get your account suspended. After 4 or 5 suspensions, it's a permanent block...

As such, many people block others simply to prevent them to report their posts. It's a defence mechanism and not a tantrum.