The recent collision of two satellites reduces the credibility of the big sky theory somewhat?
Yet given that most GA aircraft don't use TCAS and we are told we don't see most of the other aircraft flying nearby, the number of mid-air collisions are surprisingly few. Not really surprising as the chances of another aircraft flying in another light aircraft's path within 10 or so feet of the same altitude outside of an ATZ must be statistically very small. (Why are encouraged at as students to fly cross-country at only 2000 feet?)
I recently tried an experiment on FS using FS Recorder Module which allows one to replay multiple previous flights simultaneously with the current one. I arranged for up to 20 "Cessnas" to fly up and down at lease twice at 2000 feet over a 5 mile stretch motorway having taking off at 15 second or so intervals. Although some of the aircraft came alarmingly close there were no "collisions" and only occasional avoidance manoeuvring was required.
On the other hand, if TCAS is available and it helps to give vital information, why are we not all using it? If it was a legal requirement to have one then all the rental aircraft would have them fitted. Most if not all already have transponders.