On one hand, I get it. They are scientists and they have to go with what they can prove and in the absence of proof they must conclude it doesn't exist.
On the other, they are wildly optimistic or projecting their hopes to ignore human history and behavior elsewhere. Their conclusions/ beliefs fly in the face of everything we know about history and have for hundreds of years. We have civilizations because of man's need to defend himself and the knowledge a group is stronger than an individual. Since the dawn of time someone covets what another has and so they take it be force or guile. Someone is weak, someone is strong, someone wins, someone loses and club or AK-47 nothing changes and nothing will change.
There's a belief/ movement afoot today that argues a global economy will make it cost-prohibitive for nations to go to war. Nonsense. Greed and madness will always exist, a global economy may make it harder to go to war, but we shouldn't underestimate our fellow man. He is nasty, brutish, greedy, cowardly, vain, and willing to kill anyone for his ends and means. Though a cliche' by now, I firmly believe some are like a certain bandit in The Dark Knight Returns:
War is our destiny and war never changes.