I was supposed to be a lawyer defending America's decision with another student the prosecuting me, the conversation ended in a heated screaming match. Help us out Historians!
Go and pick up a copy of Studs Terkel's The Good War. That book is chock full of opinions about the dropping of the atomic bomb. You'll find that the majority view is that it was a good thing because the war ended. Over time, attitudes gained nuance.
It was either:
A) Risk 1 million Americans' lives on a mainland invasion (high projected casualties) with later assistance from the USSR.
B) Drop a reliably-tested nuclear device on select Japanese cities (thus incurring civilian casualties) and end the war with a Japanese surrender.