I am with Ryanair on this. I spent the last 20 years of my flying career doing four sector flights around Europe (and sometimes more).
Can you just imagine the chaos that would be caused if, for example, I flew from UK to Germany (for a quick turn round) and then had to go through immigration and passport control and back out my aeroplane again, to fly to Vienna, do the same rigmarole all over again, then fly to Prague just to go in and out of their immigration system before going to Istanbul and going to bed.
Can you just imagine what would happen at Heathrow if every Lufthansa, Air France, LOT, Iberia etc etc flight crew had to go through UK immigration and back out again every time they did a quick turnround?
Get real people; this is bizarre. It simply does not happen anywhere else that I ever encountered in 46 years.
It has nothing to do with Ryanair and it should be resisted at all costs.