Your argument against minimum wage would make sense if labour were inelastic. If it were illegal to work more than 40 hours per week, the total available worker

Your argument against minimum wage would make sense if labour were inelastic. If it were illegal to work more than 40 hours per week, the total available worker hours would equal the number of eligible workers times 40. But that's not how the world works. Halve minimum wage (don't worry, inflation has already done that) and suddenly the people who were barely keeping their heads above water on 40 are now no better off on 80, or they're living on the streets.