"the majority of people are attempting to, or engaging in some kind of scamming behavior in at least half of their interactions."
I think the numbers are way lower, but it is an old, archaic idea, you do good for your tribe/family - by taking from anywhere outside of the tribe. Stealing from the tribe is very bad and might get you killed. Stealing from another tribe however is not stealing, but reputable work, as long as there are no established friendly relations to that tribe. Many people indeed operate with this mindset (consciously or not)
But all in all I would rather say, that the number of people who consider all of humanity their family, is increasing.