They were free to use it and did.

Their employer, the Federal government, was free to fire them, and did.

I'm referring to the idea of striking being illegal, and the underlying attitude that motivates such legislative decision-making.

and now the country of freedom is free to deal with ATC shortages that leave people managing two runaways and ground traffic by themselves in a a major airport

ah, truly a decision with no consequences

tl;dr just because it's a legally allowed decision, doesn't mean it's a right decision

There’s a pretty big difference between “economic leverage” when it means your stores might be shut down for a couple of weeks vs. all of the people moving, shipping, etc. in an entire country.

A strike being inconvenient? Workers leveraging how crucial they are? The stoppage of work having massive impacts across the country? Huh, maybe the powers that be should listen to the workers when they ask nicely for better conditions instead.

Isn't the "inconvenience" the entire point of a strike? A strike where nobody was affected in any way wouldn't be a very effective one, after all, so the larger of an inconvenience the more likely for the other side to relent to the unions demands.