I believe the universe supports the evolution of life. But interstellar competition would inevitably give rise to a supreme species that dominates all others, just as it would on any given planet such as Earth. Note for example that the drive to colonize could come at a relatively primitive stage prior to the establishment of a global ethic. That dominant species could prevent any others from evolving, such as how the dinosaurs prevented the rise of mammals. Such a dominant species might stagnate, and force other species development to be stunted. A particularly savage species might rape the universe, rendering much of it unable to support viable ecosystems, just to grow it's own wealth. To do this on one planet might be permissible, since it is a closed system. But to artificially shift resources across interstellar distances might be irreversible on any geological timescale. Damage could easily be permanent. Much of the galaxy could be sterilized, or only viable for primitive life.

I prefer to think that it would be impossible for life such as ours to have evolved in the first place had our planet been decimated by the colonization efforts of species from other star systems. My own engineering analyses of possible starship designs, none of which were viable, indicated that interstellar distances are a fundamental barrier akin to the speed of light but more subtle. This, together with the lack of evidence for prior colonization by extrasolar species, has led me to believe that interstellar travel is impossible.

We're safe. They're safe. Until I'm proven wrong.

The question still remains as to why life should evolve on multiple planets if it is impossible for them to interact? Maybe there is a way and we haven't discovered it yet. Or maybe there is a whole different path up the evolutionary ladder that has nothing to do with interstellar travel and, again, we haven't discovered yet.