a 51% attack that double spends appears to violate the Computer Fraud and Abuse Act. i think even a mere censorship attack would qualify based on that legal theory.
whether it's enforceable is another matter. it carries a prison sentence of up to 10 years per count, and victims could sue for damages, but this is all theoretical. it's never been done, and the legal theory has never been tested in court. i assume the discovery process would be an absolute nightmare.
I have big doubts that anyone would bother to investigate a censorship attack, the authorities wouldn't even clearly see who is the victim, who is the culprit, what was the damage, and Bitcoin is a decentralized network, not a company that can go to court. In case with double spend, there will be a clear victim - an exchange or other service that lost millions of dollars worth of coins, and the attacker that made and then reversed a transaction.