The claim is that more people would be employed if the minimum were lower. It's not clearly either true or false yet, despite decades of claims and studies.

If it's true, lowering the minimum would make people currently getting the minimum worse off, but would make some people currently unemployed better off (by being employed). Plus it would have some effects, even harder to predict, in surrounding groups.

Trying to balance out those two and decide if it's worth it for society is certainly not trivial or obvious. The numbers in each group would matter a lot.