I just took a survey for a young student who is interested in astrobiology.  One of the questions was about whether or not the surveyed individual believed we were "alone" in the universe or not and why.  Here is the short answer I supplied after clicking the option for "I believe it is highly likely that we are not alone":

I'm sure most people in my profession would answer this with the traditional "waste of space" quote, but I'll try to be a little more from-the-heart with my answer.  From the years I've spent earning degrees in biology, chemistry, and now geology, as well as the time I've spent reading and thinking about myself, about our species, about our place in the universe, I have come to believe (yes, a scientist can have beliefs) that life, life as we know it and maybe even life as we don't yet know it, is extremely likely to exist in our universe outside of Earth.  With the billions upon billions of stars in our known universe, many of which we are slowly but surely learning have their own planetary systems, it is highly likely that there are other places where life may have originated and where biological evolution may have begun.  These places need not be Earth-like.  There may be a multitude of ways in which life can originate and develop.  However, that remains as well-founded speculation.  To be even more forward, there likely are many planets in our known universe which have near-the-same planetary dynamics as our Earth and which may have allowed for the origination and evolution of life as we know it.  I do not believe our Earth is rare.  I do however believe our Earth is special.  It's special because it's our home, our cradle.  One of the drivers in my growth as an astrobiologist has been is my sincere wish to understand our world better, and to maybe help humanity in understanding ourselves as we slowly begin to look out at the cosmos that lie beyond our cradle.