

Nothing legally stops you from listening. To transmit, you are legally required to have a callsign (which you must broadcast during transmit) and your callsign must be licensed for that frequency.
If you break the law, it’s highly unlikely that the FCC themselves will hunt you down and fine you. If you’re using it to talk to others on the HAM bands, they’ll likely get pissed at you for not being licensed but actually tracking you down is difficult. Using it for your own personal projects, friend groups, etc, it’s unlikely anyone would notice you at all.
A license is like $15 for life (just need to occasionally tell the FCC you’re still alive), the test will teach you some stuff, I don’t see it as that onerous to play by the rules so I’d recommend following them.
Lol whoops yeah, ARRL. I work in aerospace where we love our alphabet soup and I brainfarted AFRL.
I wasn’t trying to say that the band plan doesn’t exist for a reason, it absolutely does, some reasons which you pointed out exactly. I’ve definitely been around guys who treat the band plan like it is the law, and I imagine the original commenter had the misfortune of running into one of those guys and believed him at face value. Imho it’s one of the reasons ham radio has been dying as a hobby.