This is why finding even a extrateresterial bacterium is so vitally important to start to answer these questions. It immediately gives us exponentially more knowledge on the requirements to at least get life started. I will say the pessimists (especially the creationists who for some reason think it is somehow blasphemous for other life to exist), continuously grasp at any data they can interpret as reducing the probability, and the other side grasps at the other interpretation. But inexorably it does seem the more we learn the more likely that life could exist elsewhere.

Recently, we have found life at much higher extremes on planet earth that we was ever imagined for centuries. And we have found life not based on photosynthesis but chemistry. We have also found other solar systems despite our rather primitive tools for discovery at this juncture. And the simulations we perform make it more and more likely that many earthlike worlds exist in this galaxy and others. And in this case many is a vast understatement. As Carl Sagan used to say "billions and billions."

It is hard to believe that "intelligent" life inexorably wipes it self out, although I guess it can't be ruled out. Maybe it is inescapable at some point in natural discovery of universal mysteries by intelligences that some sort of doomsday door is opened (e.g. if every individual has access to technology to destroy all life...someone will push the button). My spin, is that I believe the opposite. Some sort of transition occurs (which could be called a singularity) which makes expansion into the physical universe irrelevant. Maybe the "superbeing" finds other dimensions or creates other universes to straddle. One answer to the Fermi paradox is that inevitably the emergent life just doesn't care and lets itself die. I think the least likely possibility is some sort of technology bottleneck.

It does seem that if we projected current man out into the universe, then the signs would ultimately be unmistakeable. Our galaxy would have "Hi there Andromeda" spelled out in moved stars. At the rate of our technological change and advancement there are no obvious show stoppers to creating dyson spheres and the like in millenia. And millenia our a drop in the bucket compared to billions of years.

I think the reason that most people don't believe there are some sort of natural show stoppers to expansion, is that we really already have technology now to start expanding. It is just that the cost is so high we don't yet make the tradeoff to do it. Bootstrapping space colonies does just seem to need some time to develop, given it is hard to find technological limitations of doing it.

"GIVE ME A PLACE TO STAND AND I WILL MOVE THE EARTH" ...Archimedes. When you see how the "lever" multiplier keeps improving over time, it is very difficult to take the stance that no one will ever be able to move the earth.