Certainly do. And I don’t think it’s all that complex either, (not the other life forms, the question of their existence ;-)
To me, it’s like when you’re catching that pre-dawn business flight. You’re on schedule, yet on the way to the airport the cabbie runs all the red lights. When you ask why he considers this an acceptable way to drive, you get, “Hey, it’s 2am pal, who’s gonna be comin’ the other way?”
My feeling is that since you’re out there on the road, and the cabbie’s out there, there’s a fairly significant chance that someone else is out there as well.
So too, with other life in the universe. We’re here, the universe is way too big for us to seriously believe that we alone have evolved into an intelligent life-form, so they’re out there too.
To complete the cab analogy, the question isn’t whether or not there are other forms of life sharing the Universal Highway. The only question is “when will we run into each other...”