I'm not trying to justify or leap to any defense, just trying to understand myself.

But I'm kind of getting the feeling that they are trying to do a catch-all.

For all practical purposes, if it was a free-for-all of people treating airports like public forums, it just keeps sliding. The reason the airport is there is to facilitate people's travel, travelers don't want to be annoyed by constant destractions, let's face it, customs and enforcement wants the least amount of chaos. The airport doesn't want to bear the continual cost of extra staff to manage. Police don't want to have a hotspot of constant nuisance calls.

I think this type of post really inflames people, but in a way it seems to have practical purpose. I'm not even sure that it implies that free speech is not allowed in the airport. Just like tacitly... Dear annoying assholes that hide behind Free Speech, go stand here.

Yes, but they can still annoy you with dumb lawsuits. Maybe this reduces those.