I never made such a claim. All I am claiming is that I don't believe there are other intelligences out there because I have seen no proof that there are. And yes, its a fine logical point. When and/or if such evidence shows up, I will likely change my mind. But until it does, I believe what I believe.
Well, I myself believe the only rational position is "agnosticism" in the matter.
IMO, there is not enough evidence, nowhere near as a matter of fact, to make a judgement either way. And science should not take things as a matter of faith.