Say someone deploys Tornado Cash to Solana, NK uses Sol-Tornado to anonymize recently stolen SOL, U.S. Treasury adds these SOL addresses to OFAC sanction list, and notifies major SOL validators, along with Solana Foundation, and Jito.

What's next - is Solana now censored?

Ok, now same question for L2s...take Arbitrum.

Someone deploys Tornado to Arbitrum, NK uses it to anonymize recently stolen ETH, U.S. Treasury adds ETH addresses to OFAC sanction list, and notifies Arbitrum Foundation & Offchain Labs who runs the sequencer.

Is Arbitrum now censored?

Of course, all this has already basically happen on Ethereum and Ethereum has currently maintained strong censorship resistance...but could Solana...could today's L2s?

Doesn't Arbitrum support forced inclusion from the L1?  If so it should inherit mainnet's censorship resistance.

It has, but since arbitrum still has a 9/12 multisig (globally and organizationally distributed) that can force a code upgrade with no delay, it is not impossible that an upgrade to censor certain transactions in case the signers feel threatened of repercussions. This concern goes away when Arbitrum is stage 2 though