Why force the nose of 737 Max down in the first place?
The main thing to avoid in aeroplane stability &amp; control, is an aerodynamic nose up moment that is not commanded by the pilot. The uncommanded nose-up moment would not auto-stabilise, but rapidly get progressively larger with increasing angle of attack, and run away to a stalled aeroplane.

During certification of a passenger aeroplane, many tests are carried out to check if the airframe does not start to have a mind of its own. 


If the pilot does not provide a control input, the airframe must return to the trimmed position.
Forces and inputs to move the aeroplane away from trimmed position must be such that there is an ever increasing force required to achieve an ever increasing nose-up position. The nose-up position must always be commanded by the flight control surfaces, elevator and stabiliser, in a predictable way.


One of the tests to be performed during certification is stick-force-per-g. Bank the aeroplane and start turning while pulling the stick back in order to maintain altitude. Then bank more and pull back more, in ever tightening turns. It must be progressively harder to pull back on the stick to maintain altitude, never easier.

It was during this wind-up turn that due to the engine configuration of the MAX an aerodynamic nose-up moment appeared, which would cause the pitch stick force to suddenly become less than expected. Not as bad as a runaway pitch, but still an undesirable situation when the pilot is still straining to maintain the manoeuvre. This is the situation that MCAS was originally designed for, to auto-compensate for this situation only. The aeroplane should always stabilise itself and manner of control must be predictable and within the reaction times of humans.

More info in the links in this question, very interesting articles which illustrate how MCAS design bloated from the original scope, under time pressure.