The parts of Linux that get integrated into BSDs should not be GPL-licensed, e.g. <https://github.com/torvalds/linux/blob/c339f4010dea8b0d754f8...> and its siblings use MIT.
https://netbsd.org/about/redistribution.html
As for being compatible. Yes, FSF considers anything permissive to be compatible with their family of licenses. However, it is a one-way relationship in that permissive code can be freely used by GPL projects, but not the other way around as using GPL code would impose further restrictions compared to a permissive license.
Yes, and free software wants to ensure it remains open. BSD's don't.
I have read the majority of Stallman's writings, I have met and talked to the man himself, and I even secured a signed poster for myself and the local computer club. But, I find both the argument that sharing the code without viral restrictions and with viral restrictions plausible as ways forward to greater software freedom. Heck, I would argue that history shows that the diversity of tactics has proven successful and that we are better off today than ten, twenty, or thirty years ago. So, maybe refrain from boilerplate retorts as we have bigger fish to fry and shut up and hack?