What, at least, is the harm in letting her swallow some food by mouth?
Because then Terri would live.
Florida law considers a feeding tube to be the same as a breathing tube and if you need either one you are then on life support.
So if Terri could swallow food or liquids on her own even if fed by someone else then Michael would have no case to let Terri die. That is the sole reason and Michael wins because he had control of Terri and he wouldn't allow the truth to be known, one way or the other.
How that is legal justice serving Terri is beyond me.