eh fair enough.  you have no evidence, and i have no evidence.
Lack of evidence to the contrary does not equal proof.
I think that the combination of factors that produced the climactic parameters neccessary for life on earth are very rare.  however, judging by how common water, the most important factor for life, seems to be (atlest in our solar system and beyond), combined with how large the universe is, these conditions should have been repeated many times over across the universe.
I think that it is pure statistics, that say there have to be many, many other earth like planets out there.