But seriously, folks, diving really is easy--if we are just talking about diving. I remember my cousin diving off the Jersey shore in the early 1960s, and, yes, his only training was the sporting goods store employee where he bought his equipment telling him not to hold his breath.
When I taught OW classes, I would introduce the pool sessions with a series of steps leading to them swimming around the shallow end while (roughly) neutrally buoyant. When they came to the surface, I would tell them that they now knew all they needed to know about scuba diving, thanks for coming, etc. After the laughs, I would say that no, I was serious. That really was all they needed to be able to do to dive. Everything we were going to do after that was all about how to prevent things from going wrong and how to manage them when they do.
So can you learn to dive without training? Heck, yes! You can figure out all the safety stuff on your own, too. What can go wrong, after all?