Evidence or argument to support this? It seems false by definition.
Tautologically, you're right. Liberal is people who wouldn't do this, therefore...
But, of people who would self-identify as liberal how many are in fact closet authoritarians? Lots!
Now here, "Most liberal" might be just talking about people still within mainstream thinking. Though many talk about not throwing people in jail for things like Marijuana, few talk about reducing sentences for non-drug related crimes (and pretty much no discussion on reducing it for violent crimes as well).
Personally, I was on the other side of the fence, until the constant evidence of the extreme suffering a large segment of the population goes through in prison convinced me that we're accomplishing immense amounts of harm this way.
In the American definition of the word.