Q: "Atomic swaps can't protect me from receiving dirty BTC. Why would any smart Monero user risk using an atomic swap?"
A: to make money.
Imagine this: Farcaster is complete. The community has built an anonymous Tor exchange/forum where traders can post XMR-BTC swap offers.
An anonymous user posts an offer:
"For sale: the dirtiest, filthiest, most high-profile 1 BTC in the world. I have reason to suspect it is the target of multiple international law enforcement agencies. Chainalysis has it banned everywhere. I want rid of it. It's yours for 100 XMR. Here is the swap id: […]"
Curious, you switch windows to your fully-synced local swap-dameon and search the swap id. It's there. It's legit. 1 BTC already funded w/ multiple confirmations. Just send 100 xmr to [address], and the 1 BTC will be sent to an address of your choice. No counterparty risk.
You're unsure and hesitate for a moment. But you wait too long, and the console shows the swap listed as Pending: XMR sent in tx pool.
Some anonymous, unknown individual out there took them up on the offer. Best of luck & godspeed to them!
(note: it's more likely that the coin offer posting would read more like this):
"For sale! 1 perfectly clean BTC, ✓ VERIFIED ✓ LEGIT, I swear there's nothing wrong guys, it can be yours for just 200 XMR! I'm overpaying just cuz I think Monero is real neat. swap id: […]"
Obviously, in all cases, you will always assume that all swap offers are in exchange for the dirtiest, stankiest, least-fungible BTC in the world. It's up to you to take your chances on washing it as best you can.
I personally am excited to see the secondary xmr economy develop, where it is always sold at premium prices. Dirty BTC will run amok in atomic swaps, which is why it will be up to YOU to demand a substantial premium that suits your risk tolerance.
Price accordingly, and the atomic swaps exchange will thrive.