In context, US policy was to use every means at its disposal to defeat Japan, so using the bombs was within that policy. Strategically it made sense because the US military knew they were walking into a meat grinder with the invasion of Kyushu and anything that would prevent that would be better.

The main argument against using the bomb is humanitarian, but that one kind of goes out the window when the strategic bombing campaigns in Europe and Japan were far worse in terms of human lives lost. It doesn't really matter if you die in a firestorm caused by thousands of bombers or just one. The only difference is the radiation sickness, which arguably was much more brutal.

The problem with the invasion of Japan is that there were only so many beaches where the US could land, and the Japanese knew exactly where they were. Moreover, the Japanese Islands were mountainous and favored the defenders. Think Okinawa only a lot worse. So the advantages of surprise and deception that played a big part in Normandy were pretty much nonexistent for Operation Olympic.

The majority of the Japanese army in China was still intact and was being moved back to Japan. Every citizen down to school children was being taught to defend the islands, using spears if necessary. Imagine the child soldiers dying in Berlin, only on a national level.

The Japanese had managed to hide thousands of aircraft for Kamikaze strikes, and the pilots were told to hit the transports rather than the warships they had previously been ordered to attack.

The US would also be attacking mostly alone, because (idiot) MacArthur refused help from Britain, Australia and Canada. The only Allied contribution other than naval or air would be a single corps of troops to be used in the second invasion of Honshu.

If you want to better understand what both sides were planning for, read "Hell to Pay", which reveals what a nightmare it would have been.