It seems a pretty big leap in logic to say that if there's advanced civilizations out there that would have flooded the universe with space craft and colonies. I think he's not really grokking the mind-boggling size of the universe. It is a fun argument, though. I think if there is a Great Filter, then it is ahead of us. Life is common. We as a race are doomed. The universe will not even shrug and other civilizations and races and forms of life will rise and fall. It's all good. We will eat and sleep and make love and enjoy ourselves... and then die. I don't find this pessimistic. I find it glorious! OR -- civilization advances to the point that everyone can upload themselves into a digital existence that is far better than reality. No one would want to expend resources to travel to other planets because you can exist in a magic world of unlimited possibilities for a fraction of the cost. We may well be on the edge of that now.