OBL had literally, from his own mouth and hand, declared war on the USA. He also said he would not distinguish between military and civilian targets, we were all “combatants” to him because we voted for war-mongers etc.
So killing him should not leave you torn. At all. I’m not aware, in your example, that Castro had declared a terror war on the USA, and followed it up by bombing embassies, the WTC etc. Apples and oranges.
It’s not that I feel bad about Osama being killed. It’s that I am uneasy about a world in which the assassination of political leaders becomes frequent. Although I’m not sure why. Maybe a world in which war was primarily conducted through efforts to decapitate the other side’s leadership would be less bad than one which aimed at mass casualties.