Think of our daughter, if you have one. When you make it personal, it’s a lot easier to be merciful.
I have both a son and a daughter and have raised both not to be criminals. If one were to kill their child before or after birth they would have to be punished.
Next time you read about a serial murderer or a thief, think of your son.
We do have to make laws that are applicable to everyone’s son and daughter - and with a “there but for the grace of G_d go I” attitude - both for the victim(s) and the guilty. However, we shouldn’t decide on the enforcement of law on a case-by-case or emotional basis.