> Imagine another country was delivering opium to your country and the dock workers went on strike to stop it. This same dumb argument would apply.

Imagine if another country was delivering opium to your country and the dock workers get a cut so they have a financial interest in keeping the opium flowing. You outlaw opium and the dock workers strike grinding all commerce to a halt until you un-outlaw opium.

Monopolies are generally bad. It gives the monopolist nigh absolute power and absolute power will often be abused.

What are most labor unions but monopolies on labor? It would not be so bad if there are competing unions but often there is just one.