Onion sites have been taken down too. They're still on a server somewhere. Also, the darknet is not "illegal".

Honestly I think Lightning itself is enough of a "mixer" that government could try to ban it on AML grounds, or force KYC compliance as you say. But that's only for custodial.

The way I think about it, the privacy gains, like with mixers, are statistical. It's like plausible deniability. If regulators force KYC whitelisting, they have to do it to some percentage. It would be like trying to ban all physical dollars that have ever been used for something illegal. You can say some serial numbers are tainted, but only temporarily; once they are diffused, they must again be valid for payment.

Also, a mint isn't "locked" to an IP address or particular lightning wallet. They have an independent, verifiable identity anywhere they "go".