I like the second paragraph- I'm a fan of the multiverse theories althoyugh I usually think of them as being all from one point of existance.
On topic though, we have seen the planets, sampled moon rock etc. We know that other bodies have rock, at least. Granted we haven't seen anything like the Earth, except fossils on Mars, so I guess you could say we may be unique. Quite aside from the fact that that dooms us all to eventual destruction, I think that it's naive. Granted you might think I'm naive for believing in moon rock but hey, what the hell.
Here's something; lets say Earth is flat, but Mars is round. Could there ever have been life on a flat world?