how is that enforceable? you can't determine what the encrypted communication is.

Same as anything in amateur radio. There'll be a lot of hints at what you're doing from the shape of your broadcasts, and there's a lot of amateur radio enthusiasts that'll call the feds on you if they get a hint that you aren't following the rules.

radio enthusiasts are fans of the fed?

They're generally very into enforcing the FCC rules, and calling the feds is one mechanism for doing that.

Here's an ARRL article from 11-2016 (re the shutdown of 11 FCC field stations) which details plans and motivations.

https://www.arrl.org/news/fcc-special-counsel-laura-smith-sa...

In a more recent post (which includes good suggestions for experimenters):

> The ham bands aren’t full of whacked-out haters looking to get rid of everybody else, but hams are very accustomed to people using the bands without a license or not following the band plans, causing interference problems.

https://thesilicongraybeard.blogspot.com/2020/09/a-ham-radio...

Usually the 'self-policing' by hams (it's usually very effective) is done gently. They get that the frequencies are free of $$cost, and don't want to lose (any more of) them.