Was World War II Unneccessary?

A new book out is claiming it was. Nicholson Baker writes in his book Human Smoke that it was the belligerence of Churchill and Roosevelt that allowed Hitler to solidly his power and authority in Germany and a major reason for the war.

Now I have often rolled my eyes at the level of adulation often given to World War II as if it was this neat little event where we, the good guys, just rolled up our sleeves and said, "We're going to teach the bad guys a lesson." The Allies certainly committed some atrocious acts and we should be able to look back on them with a critical eye and objective judge our actions without blindly resorting to, "Hitler was evil. We were the good guys fighting him so we could do no wrong."

However, it is ludicrous to go so far as to say that non-violence would have successfully dealt with Hitler as Baker tries to claim. Taking human life should never be done lightly and should without a doubt be the absolute last resort, but I don't think there's any doubt that the Nazis aligned with the Japanese presented a grave danger to the entire world and a military solution was the only one that was going to work. We can quibble on the details of how it should have been carried out (was it necessary to carpet bomb German cities? Drop the atomic bomb?), but you can't make a serious argument that holding hands and singing Kum Bah Ya would have curtailed Hitler.