It is if you use it to maliciously interfere with someone else's network.

I suspect that the definition of "maliciously interfere" is the tricky part to define. In this case, the convention center was effectively DOS-ing its visitors/customers to vendor-lock internet access, which is as clean a case that a court could receive.

AFAIK (and IANAL) in the USA (IANAL in other countries either :)), some areas even criminalize the act of intentionally joining an open wifi, so I imagine a court could be extremely broad in its definition of "interfere" -- in our technophobic atmosphere, I wouldn't be shocked if this extended to scanning for SSIDs outside of the context of the OS.

The hotel did not own the networks they were interfering with, that's why the FCC is getting involved.

> so it seems it can be illegal even if you use on your own network, which is absurd

They used it on other people's networks and their wifi APs. If they only DoSed their own APs, no one would care. You are allowed to DoS your own APs.

aircrack-ng itself doesn't send anything, so it wouldn't be affected by this. Its sister tool aireplay-ng however can be used for exactly this kind of attack, and that is illegal.

Nothing has changed though, those laws have been in place since soon after the invention of radio.

It always has been