Of course, it's true an evil regime can just accuse random people of crimes and arrest them.

But it's much worse if they manage to identify actual critics, people who actually defied them in some way.

The regime that strikes out randomly, probably that ferments opposition, right? The revolution that eats its young is a lot less scary than the revolution that consistently eats its enemies.

To have evidence to pacify some of those still on the fence about the regime vs out right in favor? The anti-regime will always be anti, but if you can keep those undecideds pacified with attempts at evidence/fair trial, you can make it look like majority in favor