Are there armed guards preventing you entering the forest and living off birds you kill with your hands and sleeping on pine needles?

Well, yes, actually. Not without reason, but literally, yes. Typically some combination of public property, private property, and wildlife/safety regulations stop that from being a long-term solution. Depending on how far away from society you go, you can escape scrutiny for a time, but you’ll never be safe from the threat of the cops rolling in and destroying whatever you have and dragging you out for trespassing or violating public land ordinances.