Of course the police arrest peaceful individuals to send to prison.

Arresting non-peaceful groups is very difficult and dangerous.

Further, since this is for the slavery system prison industry, then of course you want peaceful individuals.

Japan is a very strict country. And laws, once formed are set in stone for generations. This means very little crime in most areas of Japan, but it also means that any unjust laws are just... "that is the way it has to be"