> So, what you’re saying is that a decision you make as, say, a 17 year old is one that you must stand by for the rest of your life?

That's basically the way it is anyway. If you go out in public (physically or virtually), you've lost some control over how long-reaching your actions might be. If you do something stupid in public, you can't prevent people from posting their videos/photos of it, or just talking about you. The internet is no different. While you can get your stuff removed from some places, you have no control over it generally speaking. Somebody might have screenshots for example.