Atheists are not believers, they are observers. Scientists don't believe in God because they observe that he doesn't exist.
No one claims to have observed that gods don't exist. All we say is that no one has observed any empirical
evidence that they exist. Those are two quite different things. The most cogent rationale for the existence of gods is that since we are still baffled by some of the workings of the universe, it must therefore be under the control of supernatural beings. That is not evidence at all, merely an extraordinary assertion with far less than extraordinary substantiation. Therefore, according to the scientific method, it has been adequately peer reviewed and found lacking and we are under no obligation to take it seriously as a hypothesis.
Scientists are free to believe whatever they want so long as it does not contradict "truths" that have been established beyond a reasonable doubt. Many scientists believe in gods and many don't. Those who do, do not claim that their belief is a valid scientific theory, it is merely in the class of a hunch or a hope. Those who do not, cannot claim it as a scientific theory either, because science only deals with nature: the observable world. The supernatural by definition is external to this, if it exists at all.
Why can't ethics and morals be derived from reason and logic?
They increasingly are. Homo sapiens continues to use his uniquely massive forebrain to override his pack-social instinct to advance civilization (as well as other primitive instincts such as the archetypes that are the basis of religion). His code of conduct advances right along with it, being derived steadily more from reason and learning and steadily less from instinct.
You use the word might. You tell me, how many innocent Japanese might have been harmed by the invasion? Are you so sure the Japanese wouldn't have surrendered before we reached 150,000 deaths on both sides? (To add to that 150k body count, you also have the survivors who lived with severe medial problems for the rest of their lives) PS: I'm agreeing that the nuke was the fastest, most logical way to end the war. I'm just not so sure it was the path to the least suffering that you claim it might have been.
Hindsight can always be used to second-guess decisions, especially those made under the pressure of war. However, what I have read about the reasoning behind the nuclear attack says that at the time absolutely no one agreed with your hypothesis. The U.S. would have had to send the largest invading force ever assembled to conquer the Japanese homeland, and our armed forces alone could easily have taken 150,000 casualties. Japanese civilian casualties were estimated in the tens of millions. The least conservative but still reasonable prediction I've come across was that three-fourths of the population would have died, counting second-order effects like starvation and untreated wounds. It's quite likely that defeating Japan by conventional warfare would have doubled WWII's sixty million body count.
Don't forget their code of honor. I have often made the morbid joke that the Japanese would have fought until the last six-year-old girl was gunned down while charging a batallion of U.S. Marines with the samurai sword she plucked from her dead father's hands. No one who fought on the Pacific front in WWII regards that as a joke.
The point of obliterating the unsuspecting civilian populations of two cities of minor strategic value was to impress upon the Japanese that they were fighting a new kind of enemy with no sense of honor, one that was guided by reason alone. As I have stated before, this was almost a textbook example of terrorism. We
terrorized Japan's civilians into supporting our cause--winning the war by Japan surrendering rather than by Japan ceasing to exist as a nation--because we had no other way to enlist their support.
It was one of the very, very few times that a campaign of terrorism was ever successful. And it illustrates the fact that history is written by the winner, because history does not call the attacks on Hiroshima and Nagasaki "terrorism."