The American Army Air Corp conducted daylight raids against factories and other military targets to try to spare as much non combatant damage as possible. Bomber Harris thought that the US was insane for not killing as many "Huns" as possible, and the RAF mainly operated at night against whole cities. That is why Harris was not very welled liked among his peers of the time.
In the eastern theater, the US firebombed Japanese cities. The death toll was higher in those attacks than in the two atomic bombings. In a culture of wood and paper houses, a few napalm bombs caused a firestorm.
Targeting of civilians is a dirty way to fight, no matter who did it. I can't really blame either of the Allied commanders for doing it though. They were under enormous pressure and probably felt it was them or us.
The RAF operated an night because it saved bombers from being shot down.