Two things. First, Sagan's conclusions are completely reasonable if you are completely convinced that life requires no designer... if it's a function of pure chance then the numbers make it implausible that life would only exist here. If you look at the complexity of the simplest single cell organism, just the physical structure, I'd say its near impossible to imagine that coming together by chance, but when you realize the 'programming' that it takes for that system to function, well, IMO to believe that came about by chance requires an enormous leap of faith. Not trying to start a debate, but also not willing to sit by silently as though we all agree with Sagan.
Second, there is no such thing as a physical infinity. Consider that space is the void between physical objects, but for there to be an infinite amount of space then everything that "is" would have to be space, because if not there could be more space than there is, but since infinity plus one is irrational this is not possible. Glad I could clear that up for ya (lol).
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