The issue isn't that they're Turing complete or not, but that people are hacking programming language features on top of YAML in the worst conceivable way. Like

The issue isn't that they're Turing complete or not, but that people are hacking programming language features on top of YAML in the worst conceivable way. Like if you were regular sadistic, you would say "I'm not going to write Python, I'm going to write Python's AST in YAML", but if you're advanced sadistic you say "I'm not going to write Python's AST in YAML, I'm going to make up an AST for a programming language that doesn't exist with bizarre and inconsistent semantics in YAML (YAML has lists, but I'm going to make people pass lists as comma-delineated strings--it'll be a riot)".