Dropping the single available parachute division (the 7th) into England on its own would have been suicide. This division had just sustained heavy casualties in their drop into Holland and was not that large to begin with. To drop the full unit would have taken about 3 lifts with available Ju 52 aircraft due to losses in the French campaign.
The entire unit would have amounted to about 6,000 men with no heavy weapons to speak of.
The British response would have been to commit the fully motorized, fully equipped, and well trained 1st Canadian Infantry Division then in Southern England to crush this drop. Given that this division had about 25,000 men in it and could have been supported by various smaller units, including armor, the Germans would have been in a very bad spot.
This is just another German improvisation done without thinking through the situation. It would have been disasterous.