Mi She'eyn Bo Deah Assur L'eracham alav

The Maharsha in Sanhedrin asks why is one who has no da'as worse than  a dog which we are commanded upon which we are commanded to have mercy.

R' Moshe explains that the world was created with "Din" and Din is the ultimate Tachlis of the world. However, because Gd saw that the world could not exist in perpetuity with only Midas Hadin, he therefore added a measure of Midas Harachamim to work together with the Midas Hadin. We see that Midas Harachamim is there to give things a Kiyum in the world. One who has no Da'as does not have a Kiyum intrinsically. No amount of Midas Harachamim can change that. It is therefore forbidden to use Midas Harachamim in a circumstance where it cannot perpetuate its subject.