Its naive to think in an ever expanding universe that we're the only planet with any sort of life. Even if its a planet that is just a forest, or mold, or bacterium, or whatever. The universe has been expanding for billions of years.
I also don't buy that water is what's needed for life. For us, sure, but that is what this planet is mostly made up of. Carbon and water, so its no wonder we're carbon based life forms that are what? 70% water or whatever?
Who's to say that some planet the basis of life there is liquid mercury and the gas form of methane or something.
I do believe aliens have visited in the past. I'm a big believer for the ancient astronaut theory that the "angels" ancient man saw were aliens, and halos were the glow from the space helmets. Dragons in Asia were space ships, etc. Have you seen the ancient art with supposed aliens?
I don't know, maybe I'm insane, but I believe.