You could say that about anyone at any time. Only fools think they can foresee all the consequenses of their actions. Can you say with certainty that things would be better for the world if we had not used the bomb? And better in what way? Can you be certain that without the horror of the bomb, that it wouldn't have been used later in a much larger war?
You think Leo Szilard and the other great scientists who shared his view were fools? You don't place different values on opinions according to the experience and ability of those who express them?
Your arguments can also be reversed. Who's to say that sharing atomic secrets with the Soviets was sure to be catastrophic to our interests? Perhaps the Rosenbergs were right? I'm sure you don't like that line of reasoning.