Exactly. REST screws with our internal matrix of "things allowed on methods." Instead of idempotent GET and mutating POST, what does PUT do? Can DELETE be run twice? I'm sure the RFC says, but it just adds additional complexity on our heads (which we may want to override on a per-case basis anyway).
GET alone is safe -- it doesn't have side effects.
The results of POST and PATCH depend on the current state of the resource they effect, so they aren't idempotent.
The results of DELETE and PUT don't depend on the current state of the resource they target, so they are idempotent.
> I'm sure the RFC says, but it just adds additional complexity on our heads (which we may want to override on a per-case basis anyway).
If you don't want to use the semantics defined in the RFC for a particular method, use the method with the right semantics.
