Oh boy! What do you not understand about what I am posting? They make it explicitly clear in the film that they kidnap and brain wash troopers from an early age, how much of the force or brain washed babies we have no idea but we now know at least some of the fighting force comes from them. Additionally, we know from the prequels that some of the fighting force is or was made up of Clone Troopers. Now, in the OT all we seemed to be shown were that they were Space Nazi's who we can assume volunteered or were conscripted. The extra knowledge that Stormtroopers could potentially be brain washed babies along side the "reeducation" bit introduced in this film and the entire arc of Finn's character humanizes Stormtroopers and shows they aren't all evil.
Thus, as I said before, it's hard to revel in their deaths when some of those Troopers are potentially brain washed, kidnapped children, who were never given a name and taught nothing but how to kill.