Yeah I don't like it either, honestly. I could see a large group succumbing to cannibalism if they were starving to death while also dealing with assholes messing with their group. But their reaction to a few bad guys was, "fudge this, we're eating EVERYBODY!" Never seen that before in history or literature.
While I agree, the sociopathic personalities seem excessive. We've seen that from countless examples of popular psychology that people do messed up stuff to other people, when given the power. However, their initial modus operandi wasn't just to "eat everybody". I think they just realized they couldn't keep themselves going any other way. By this point, food and ammo are scarce in this world and the knowledge to produce it gone. So when it came down to dying or living, they gave those who found their way to Terminus a choice to become a part of them, and if they refused... well, they became a part of them in a worse way. TW alluded to trapping to survive and that's exactly what Terminus was, a funnel trap.
And based on the type of people there, it was the most effective they could muster. Its easy to talk about making spears, and rabbit traps and shit like that but the reality is, being consistently successful in both creating and using those primitive techniques to catch wild game is low even for a survivalist.
Now throw in Bob from IT, Jane the Bank Examiner, mom, dad, and 50+ other random folks... that's a lot of rabbits to throw rocks at.
BTW, knowing your opinion is already made, I'm not trying to change your mind. Its just fun to talk about.