[contravariant]

The short answer is that it's up to a judge to decide that, up to the law what it's based on and up to the people what the law is.

Sure there is still some leeway between only letting a judge decide the punishment and full on mob rule, but it's not a slippery slope fallacy when the slope is actually slippy.

It's fairly easy to abuse the leeway to discriminate to exclude political dissidents for instance.