Sentimentality. The world is a big place filled with billions upon billions of souls. If a good person must die, or a town be flooded, or a species go extinct in service to the Plan, then so be it. We can't save everyone. Heaven awaits the deserving. Paradise on Earth must be earned.

[ Castiel's speech is never entirely natural-sounding, but this especially comes across as something he's repeating after hearing from someone else, time and time again. ]

I put one man's suffering before my mission because I made the mistake of growing too attached.