One of the most noticeable characteristics of thoroughly modern people is that they have an absolute abhorrence of violence (when they can see it). One of the other most notable characteristics of thoroughly modern people is that their philosophy utterly undermines any moral restraint on violence and also eliminates all possibility of rational reconciliation, leaving power the only relationship between people. This may not be a coincidence.
In particular, it may be that people will only indulge in being modern (Modern philosophy, post-Modern philosophy, etc) when they feel protected from the violence which is its natural consequence. An analogy may be the various stupid ideas children will engage in as long as they’re not the ones paying for things. (Things like payment should be based on the amount of time someone puts into a job rather than the quality of their work.)
In like manner to how being vegan is a luxury good only made possible (to the degree that it even is long-term possible) by advanced technology and massive trade infrastructure, believing that morality is just an evolved set of preferences where none are any better than any others may be a luxury good for people who have an effective security force that does not believe this ready to ensure one’s safety. Or like how having a philosophy that only works for non-reproductive people is a luxury good for people with a steady supply of converts from reproductive people.