What I read from your post here is that GraphQL is safe by default and would require effort to make it dangerous while Datalog is dangerous by default and would require configuration to make it safe. I know which one I'd rather put on a server.
You have read that incorrectly. A Datalog/Prolog query does not define new rules. That's like calling arbitrary code on remote machines. You would never allow that.
But IF you were allowed to define new rules, THEN you could simulate a turing machine or create infinite reductions.
