I think I've spotted a trend here.
When I do this kind of theorizing I start with a lifeless universe, and try to work forward to a theory that explains the present without as few unsupported assumptions as possible. I see that there is no particularly convincing evidence that there is anyone out there, so I think "well, there must not be anyone out there". When some SETI enthusiast brings up the Drake equation I merely note that a list of unknowns does not constitute evidence - we know essentially nothing about how easy it is for intelligent life to evolve, and we therefore can not expect to predict anything from such an analysis.
Robert, OTOH, seems to start by presuming that the universe must be filled with sentient life. He then works backwards from this point to construct ways of reconciling this assumption with the fact that we see no evidence of intelligent life. He searches the universe of possible SI behaviors for some set, however implausible, that might give that result, and then treats that set of assumptions as if it were the simplest possible explanation for observed facts.
This leads to some remarkably pointless debates. I note that some particular point requires you to make a whole raft of assumptions about the nature of SI civilizations, and ask for evidence that these assumptions are correct. Robert, taking the existence of said civilization for granted, replies that it is the simplest explanation for the observed universe and therefore *I* should have to provide evidence that they are wrong. We can go around like this forever and never get anywhere.
So, why don't we start at the beginning. I look around our corner of the universe, and see that I can explain all of my observations quite well without invoking extraterrestrial intelligence. Why, then, should I add in the complicating assumption that there must be SIs out there somewhere?
Billy Brown, MCSE+I
bbrown@transcient.com