Re: Why not just disable the system and put the planes back in the air?
What Kubla Cant mentioned is the main issue. MCAS was supposed to "fix" the nose-up pitch instability at low speeds when approaching a stall. Any pilot should be able to solve this in NORMAL conditions, but when you've been in a holding pattern in Class 3 IFR conditions for 3 hours and starting an approach in busy airspace a pilot is likely to be in less than perfect condition to keep the nose from suddenly rising if the airspeed drops due to windsheer for instance.
The thing is that this aircraft likely wouldn't even be certified as Airworthy without MCAS. It certainly isn't a system that can be just left out.