Because, if you are living in a community, and one young punk wants to destroy the community, and won't listen to advice and won't stop their harm, then you have to use control over others, and the community has to authorize such use of force.

The tribe kicked out people.

In the future, this planet will have to decide what to do with psychopaths and sociopaths. Other planets do not suffer them to exist, they are killed. Others wipe there minds with electric-shock therapy something something.