[JoshTriplett]

Do you license your code under a license that doesn't require any form of attribution or preservation of copyright notices? (Even permissive Open Source licenses typically do require that.)

If you do, then by all means they're welcome to use it without attribution or preservation of copyright notices, per the terms of the license you used.

But for all the Open Source code, even permissive Open Source code, that does require attribution or preservation of copyright notices, that's still a license violation. People don't often think of permissive Open Source licenses as something that can be violated, but they absolutely can be.