Were the shorts illegal? I keep seeing the accusation but I don't think it's possible to short sell a stock that you have not borrowed.
There isn't actually any evidence the named hedge funds were engaged in naked short selling. For the most part, people seem to misinterpret short interest and failure to deliver data as an indication naked short selling occurred.
It's quite clear naked short selling is possible and thus happens sometimes. I'm very dubious it's the case in Gamestop's specific situation. My specific claim is "naked short selling is a thing that exists", which is readily provable.