Worse than that, even.
They think like upper middle class college-ed liberal Americans.
Some particular pet peeves.
Few or no gender roles. Look folks, in a pre-modern economy there are inescapably logical reasons for men and women being treated differently. It isn't just that the men are being mean. And sexually liberated women in such a society get knocked up and punished with a child, which puts a real crimp in her non-traditional lifestyle.
An extreme variant of this is the female warrior/mercenary. An exceptionally capable woman warrior might go toe to toe with an average male warrior. She meets a better male warrior and she's toast. If you insist on the female warrior, at least bother to provide some backstory for why she is able to compete with men. Don't just ignore the physical differences between men and women.
All premodern societies we know of are deeply involved in religion and/or superstition. I realize modern readers are uncomfortable with this, but again bother to provide some sort of reason why your pre-modern society isn't religious.
One of Tolkien's major flaws, IMO. Not a trace of religion in hobbit society, and not much elsewhere. In LOTR, that is. More in Silmarillion.