...that life started on earth almost as soon as the planet cooled off. This, plus the detection of organic molecules (including amino acids) and other chemical precursors to life in meteorites and in the interstellar medium suggests life is not a weird, one-off phenomenon, that it tends to pop up easily and quickly wherever and whenever conditions allow. It appears that habitable planets are very common in the universe, too. Life must be common throughout the galaxy.

The bad news is that we're talking microbial, single-celled organisms. Complex multicellular organisms didn't appear in the fossil record until the so-called Cambrian Explosion, about half a billion years ago. They very quickly dominated the earth, but it seems that the step from single to multicellular life didn't occur until three billion years after life first appeared, maybe longer. It appears to be a real bottleneck in evolution, much more so that the appearance of microbial life.

This suggests life is very common in the galaxy, but that complex life
is much rarer, and much more vulnerable to astronomical catastrophes and planetary disasters that hit all planetary systems periodically.

It took half a billion years of critter evolution and relative stability on earth before one species arose capable of building spacecraft and radio telescopes. Unless intelligent races tend to survive a long, long time, this tells me that its very unlikely there is more than one in the galaxy at any one time.

I don't know about you, but I find that terribly depressing. If you could talk me out of this conviction, I would be eternally grateful.