Regardless of a mandate, people will do what they do even if it's not in their best interests, or in the interests of their loved ones, or the interests of their neighbors. They will smoke in public places, they will goto work sick, they will drive drunk. Frankly put, people can be jerks. So you put a mandate out there, and you do your best.

Masks work. In areas where mask utilization is high, there is good air filtration and people follow distancing rules, the spread is slowed.