Al summed it up better than I could, but I like to add that the Allies had already experience with a conditional German surrender after World War I and look how that turned out - a "stab in the back" myth, the militaristic institutions of Germany mostly intact and rearmament and a new war in 20 years. It's quite understandable that they didn't want to repeat the experience.
And in any case, no surrender - either conditional or unconditional would have happened while Hitler was alive and considering the effectiveness of the German resistance...
The conditional surrender in 1918 failed because the resulting treaty was one-sided and pissed the Germans off, leading to Hitler.
That is untrue. It failed because the spineless leaders of France and Britain refused to defend the treaty. It was actually quite reasonable, considering some of the demands made - for example, the French wanted the new border to pass along the Rhine. And it's the depression led to Hitler's coming to power, after all he had no success at all before that.
I take it you've never heard the joke about Hitler being born in Versailles?
No. Can you tell it?
At a Nazi rally, someone asks "Where was Hitler born?". The other person says, "Versailles."