There was a thing, but it didn't happen often, where a GPL advocate would take an MIT or BSD license project, make some additions, license their changes under the GPL, and effectively copyleft their release of the combined work.

I'm not a lawyer, but I don't think the law is simple.

Code exists in the Linux kernel that is licensed under permissive licenses. This works because (some) permissive licenses contain no restrictions incompatible with releasing the code and/or derivative works under the GPL.

This is why the original BSD license (with advertising clause) was incompatible with the GPL, while BSD without the advertising clause is not.

"Public domain" is not a license, and has different meanings in different jurisdictions, and thus it can be useful to release code under a license even if the intent is unrestricted use.