"Have you not heard of radar surveillance and air traffic control?"
Geoff, obviously...
Have you perhaps considered that this control is ineffective against fast moving powerful aircraft that are a little more dynamic than your avg civil aircraft. Separating a package of fastjets in the middle of an exercise against a slow moving interloper, is a laughable suggestion. These are not benign constant altitude/spd separation conditions. Were you not a controller ?
Further, not all threats mentioned are related to keeping aircraft from swapping paint. Think weapons, lasers, jamming, high energy emitters. The bottom line is Restricted areas are essential, and for good reason are often out away from populated areas which don't permit uninvolved aircraft.
You can exercise freedom of navigation - what do you think the bear bombers in the cold war did... exercised this right, didn't stop them from being intercepted by F-4s every day off the coast.