Airplane autopilots will happily fly into other airplanes
"No. Most (if not all) have ACARS installed."
Rubbish. None of the aeroplanes I flew had TCAS. They had various single axis wing levelers (basically a gyroscope and two elastic bands) or maybe two axis.
The subset of airplanes that is 100 seat multi engined jet airliners is quite small and certainly not "most".