The core of it is humans mostly don't want to help other humans, unless they're part of their specific tribe/village, to which even then it's just put them in a jail cell or off them, problem solved. The simple competitive nature of survival in the Animal Kingdom leads to assumptions and hard-lines of what is acceptable, and hey, if one person is believed to being incapable of giving back, just get rid of them, more resources for the tribe. Of course, this has changed in post-agrarian civilizations over time, but the fact that there's so many more people around that have these contribution issues, probably due to medical / technological advancement or society being humane, makes this sentiment from the populace even more misanthropic.