In a comment to a Marginal Revolution posting, Mike Huben says that the "destruction of jobs by minimum wages" (his scare quotes, not mine) is essentially unmeasurable. He adds "I'm leery of believing either of those conservative excuses. I'm much more likely to believe that the rich want to get good servants cheap."
I hope nobody thinks I'm taking advantage of Mike by asserting that he thinks minimum wage laws create no unemployment simply because said unemployment is essentially unmeasurable. And yet, the noise caused by a tree falling in a forest is essentially unmeasurable. Does that mean that trees never fall, or that, when falling, they make no noise? Far from it. We can see that trees have fallen and since we hear a great noise when one does fall, we must assume that trees that fall when we're not watching also make noise.
Thus, we have to assume that minimum wage laws cause unemployment even though the unemployment we observe in a society cannot be tracked back to the existance or passage of a minimum wage law. Or, at least, if we are to be honest people we must make this assumption.