>Remember, the question is, should we have fought WWII?<
No the question was did we have to?
The answer is yes after France and England made the mistake Pat pointed out.
On September 2nd 1939, it was not clear that the USSR would invade Poland and the Baltics. Britain and France could have invaded Germany in late 1939 or 1940, but failed to co-ordinate. Worse, they were not as well armed as they should have been.
We can only speculate whether or not Hitler would have wanted to conquer the world if France and England hadn't made those mistakes. My guess is that he would. . .these 'mistakes' would not have made Hitler change from wanting to only take over a few piddly little countries to wanting to take over the whole world.
In other words, we would have eventually had to fight Hitler anyway, and how many MORE would have died if we had waited even longer than we did?