They do have to be if they want to be approved by the FCC.

And btw Kessler syndrome applies to any orbital band. You've got the logic backwards. Kessler syndrome is usually only considered a threat for LEO because that's where most of the satellites are. But if you're throwing million(s) of satellites into orbit, it becomes an issue at whatever orbital height you pick.

Is sort of somewhat handling 10,000 by enabling them to make orbital adjustments more quickly. By the time you have a million, you will run out of prop way too quick.

Sorry I misspoke, you're totally correct. What I meant to say was it's only a problem if they're orbiting around the Earth. I've heard sun orbits mentioned as a possibility for data centers.

It would still be a space junk problem. Space is big, but amazingly not that big. If you start ejecting little hot BBs at interplanetary speeds, you are creating broad swath of buckshot that will eventually impact something with the force of a missile. Put millions of these satellites into solar orbits (I’m ignoring the huge increase in launch cost this would require, and all the other issues like latency and comms), and you could very well make trips to other planets impossible.

It wouldn’t be Kessler syndrome as you would not have a chain reaction of collisions, but the end result would be the same.

Yeah if you leave enough junk in any orbit it'll become a problem, but I don't think that's necessarily an argument not to put things in that orbit. You'd just need to not hit that critical limit where things become untenable.