Right, then you basically lose caching, since the everything's-a-POST requests would go to the wire every time. Not that I haven't considered making that trade-off.
You can use GET if you want (since GraphQL is still just over HTTP). The implementation can largely be up to you (like REST) if you want, but you get loads of things already if you opt into some opinions that libraries have established (e.g. Apollo).
You shouldn't be using fetch directly accoriding to it's creator anyway - use a high level HTTP client which handles MIME types, query string encoding, etc.
