I by and large like what he has to say, though I'm disappointed that there aren't more in-depth examples. Seriously, it says stupid aliens, but there are only a few actual aliens discussed! Here are my other criticisms:
- He doesn't consider the case of aliens who are unwilling to eliminate billions of sentient civilians in order to win the war. It seems disingenuous to assume that an alien civilization would be comprised entirely of ruthless and bloodthirsty war criminals--they would likely fall under Isaac's own category of self-destructive civilizations. We are not like that, why would all alien civilizations be like that? The US could have won within days in Vietnam, Iraq, etc. had we freely used nuclear weapons. But instead we held back--as we have in basically every war since WWII--and thus these wars dragged on far longer than they could have had the US had no morals.
- He doesn't consider imperialism as a motive for invasion. Perhaps aliens have come to spread their religion, culture, or political systems. That requires a planet with a civilization on it, and it requires refraining from destroying the civilization. Hence they have to get down and dirty with Earthlings.
- He doesn't consider interstellar novices. We could have started building a starship in the 1960s or 1970s had the world united together with that goal in mind. Which suggests that a civilization with 22nd, 21st, or even late 20th century technology could in principle launch an invasion. They would also have a much harder time invading Earth for obvious reasons.