[I have an article on the Singularity coming up at the European science/fiction magazine Concatenation in a couple months. Please visit their website ahead of time!]
I referred to the Great Filter in an earlier post. This is the idea that the great silence the Fermi paradox seeks to explain is not illusory: we really are alone. If that is the case, then since we know of one example of life and intelligence which did evolve, there must some event or set of events that dramatically decreases the odds of life evolving, becoming intelligent, and spreading from its home or at least signalling its presence. By self-indication arguments, we can assume that many other species have achieved a level of intelligence similar to our own, but that something must have happened afterward to keep them from persisting or expanding. This means it is also likely that the filter is still in front of us, i.e. that we will go extinct or at least be permanently confined to our solar system. I'm increasingly unable to discount the idea that intelligence itself is probably, usually, an evolutionary dead end.
The less interesting version of this idea is that given the way evolution works, intelligence is invariably layered on top of older systems like emotions and appetites, which were previously constrained by the limits of their behavior but once amplified by intelligence quickly destroy the surrounding ecosystem. (Essentially, the Special Agent Smith argument, but stripped of misanthropic moralizing.)
The more interesting version is that once a self-aware entity understands that pleasure and survival are separable - i.e., that its survival signal is not the same as its actual survival - and has the means to manipulate the former intentionally (ie full simulation and/or goal manipulation, which are the ultimate ends of heroin, pornography, and ideology) then the end is close. This is a much more pessimistic version of involution. Singularities could be thought of as either of these - a form of ecologic degradation that doesn't result in interstellar colonization, or as an opportunity to dissolve into fantasy worlds.
Finally, it could just be that it's incredibly unlikely that any life which evolves from matter, at the bottom of a gravity well, with a life-cycle inextricable from such an environment (needing an atmosphere, solvent, a complex web of other replicators), simply cannot expect to expand across a universe where even inside the comparatively cluttered galaxies the possible new homes are separated by light years. To a first approximation, the universe is made of vacuum with some dark matter. It may be then that every star is surrounded by an insurmountable Wallace Line.