> GET requests aren't supposed to be idempotent.

RFC 7231 disagrees.

> They're not supposed to change state in a first place.

Well, yeah, GET is supposed to be safe, but all safe methods are also idempotent.

Just because a server announces HTTP/1.1 doesn't mean it conforms to that specific RFC.

That non-RFC-compliant implementations of HTTP exist irrelevant to what properties HTTP methods are supposed to have, which is the issue under discussion.

It is compliant to an RFC, just not a specific RFC. That's part of the issue, that's simply taken for granted because of ideology.