Personally, I think if you're the one advocating for locking people in cells, you should be the one proving that it's effective.

Pretty sure your gut reaction against the punishment is good argument that it'd deter someone from doing the action that yields said punishment.

Meanwhile we do the equivalent of charging a $90 penalty for a crime that earned $100.

It doesn't have to be "effective", it just has to be more effective than not locking people in cells. If you're advocating for something else, you should be arguing its effectiveness over locking people in cells. "Effectiveness" doesn't mean anything outside of a comparison to other options.