The American military saw the results of this fanaticism in Okinawa when we lost a lot of men.
The way I see it, Truman had three choices: leave Japan surrounded or invade or drop the bomb and get them to surrender
Blockading the japanese would have resulted in more deaths by starvation than those killed and harmed over the decades by H and N
invading would have had a lot of our troops killed, yes even by civilians -- so it was an evil choice and he chose what would kill less american lives.
If Tojo succeeded and offed Hirohito before the Emperor could make his radio address, it would have been a much different story.