Absolutely, the "U" in UFO is very important.
Something I'm learning from people like Lindy, though, is that if we don't entertain all possibilities, we're probably not really approaching the matter from an intellectually honest perspective. (Please understand that I'm not saying you are being intellectually dishonest in any way. Your post was spot on.)
Something I've noticed about our fellow 'Zoners who post about such matters is that they really don't use the word "alien" very much--if at all. For the most part, they present evidence and ask open-ended, non-leading questions.
I'm personally skeptical of the alien explanation, but if I ask myself why (and permit myself to respond honestly), I find my skepticism is riddled with holes in my knowledge, presumtions and prejudices.