Huh? I disagree.
Pilots nearly always communicate exactly what their intentions are prior to and/or during takeoff and landing at G and E airports via radio, and are tightly controlled by Air Traffic Control (ATC) at Class B, and C airports. All part of the training and general practice in my (limited) experience. There are also specific traffic patterns and altitudes for every airport, if each aircraft is not directly vectored right to the ground and then directed exactly how to get where they're going on the ground by ATC. On the ground at uncontrolled airports (no ATC), there is very specific signage and protocol that every pilot learns to avoid ground collisions and radios to help coordinate this.
Between airports on cross country flights, pilots are supposed to and generally do maintain certain altitudes, depending on their heading and are tracked via transponder if they so choose (a lot do). This allows for anyone using "flight following" services to coordinate collision avoidance all over the country.
This is why we there are transponders and ATS-B. Tracking aircraft for collision avoidance.
Commercial flights above 10,000' or in Class A airspace are tightly controlled by air traffic control as well for collision avoidance.
As someone else wrote, I think drones are the more appropriate comparable here and even licensure with those comes with altitude restrictions for collision avoidance with manned aircraft (400'), rules about flying over people or populated areas, keeping in line of sight, and how far one must stay away from buildings and such. Below 400' is a free for all away from airports and populated areas, but manned aircraft aren't supposed to go below 500'.
And a higher density of aircraft in the airspace would absolutely affect the probability of a midair collision. That's like saying that more cars on the same roads wouldn't lead to more accidents. Of course it would.