But surely two parties can agree to send deauth frames between each other, for testing, development, etc. What makes this materially different?

Sure, you can deauth all you want for testing and development inside your own home or business where you arent bothering anyone. You cant "test" your deauth technology by blocking every single AP in range at a conference center, then extorting hundreds or thousands of dollars to get access to the only authorized networks. If you cant see the difference between the situations, then go read what the FCC letter says again.

edit: Imagine if this convention center entered into an exclusivity agreement with Verizon, then jammed the frequencies used by the other cellular carriers. Would that be OK?

Charging for a service that one can reject paying for is by definition NOT extortion.

I can choose not to pay you to use your WiFi.

But I can lawfully use my own WiFi hotspot, even while I am lawfully on your property. You may own the property, but you do not own the radio spectrum.

Imagine you meet an entrepreneur who has a gun and proclaimed he'll shoot everyone in sight by default, but that he provides a service in which he can exchange the bullet for the "BANG!" flag for a small fee. It's not extortion - you're free to refuse the service after all.

That's not at all the same case, you're being threatened. I'm impressed at the dishonesty on this one.

Imagine you're at a hotel, you can access their WiFi but you have to pay for it. Imagine you're at another hotel, you can use their pool but you have to pay for it. Are you being extorted? No. That's a better example.

Yes, but in your example you need to add that I have with me an inflatable pool that magically doesn't spill, and the federal law allows me to use it instead of hotel one - and I get kicked out of the hotel for actually using it (or worse, they make my magic water supply stop supplying water).

Most people buy drugs in private for just this reason.

Less glib, sure I doubt the FCC would care at all if they weren't spamming passerbys.

Presumably it being broadcast in public.

The fact that they're wilfully interfering with communications.