That's all very reasonable to me. I'm not arguing that the lack of alien radio signals indicates the lack of intelligent alien life, rather that it is the only

That's all very reasonable to me. I'm not arguing that the lack of alien radio signals indicates the lack of intelligent alien life, rather that it is the only realistic means of identifying a post-industrial civilization from such a great distance. "There could be alien dolphins orbiting Alpha Centauri" doesn't mean a whole lot when they can't do anything that would make their presence known to us 4 million lightyears away.