Quote Originally Posted by RandBlade View Post
I find the assumptions behind the theory of a Great Filter deeply flawed. There is an assumption that life would both be able to spread through the universe and would want to.

While self-replicating machines etc could be created, what would be its purpose? Life spread across Earth because it was to the advantage of those alive then, what immediate purpose does it serve to send out self-replicating machines that would never return home?

As I said, the very notion of universal colonisation could be false. If FTL travel is impossible then colonisation may be implausible. In which case there may not be a Great Filter as sentient life could be abundant throughout the universe but undetectable to us.
The Great Filter is just the the main thing that stops dead matter from giving rise to life that expands throughout the unverse and persists forever. It could be anything (almost, we've ruled out a couple things), and we may or may not be past it already.