There are some people who are a persistent threat and menace to others. There are 3 ways that society has dealt with them:
Execution
Banishment
Imprisonment
We are trying to do away with execution, so that is not a real alternative. Banishment really doesn't work in the modern, connected world. That leaves imprisonment. However, within prison, you also have a society, and then the question becomes, how do you deal with people who are a threat and menace to other prisoners and guards. Again you end up with the 3 options. Following through, you eventually end up with either solitary confinement or execution as the solution to people who are a persistent threat and menace to others.
Is solitary confinement over used? Yes. But I have not heard a really good alternative.