If you get banned from the Steam community for spamming/harassing/being awful your game library is still there. Even if you get banned for cheating in a game, you only lose access to that game and not the rest of your library.
Support did restore it, eventually. I got the impression it was a one time mercy. This was back in 2010 so their policies may have changed.
"This account has been disabled as a gift subscription that you recently accepted in your account has been reported as fraudulent. The subscription has been removed. We will make an exception in your case and reactivate the account at this time. Please refrain from accepting Steam gifts from unknown sources in the future."
Putting risk on buyers of "stolen goods" is normal, so I wasn't upset at Steam for that part. But having the entire account impacted is another story.