This trope concerns itself with things from the past that seem like a huge load of
Values Dissonance. They may be laden with, say, a
Rose-Tinted Narrative or a
Historical Hero or
Villain Upgrade.
Only... it turns out it was comparatively Fair for its Day. Maybe the
Historical Hero Upgrade or
Historical Villain Upgrade wasn't that unfair a reflection on the person's views. Maybe the
Rose-Tinted Narrative just wasn't rose-tinted enough for its original audience. Maybe it was even ripped apart in its own time for being downright insurrectionist and was brave to go as far as it did.
This doesn't automatically make the work immune to criticism: something less dissonant than its contemporaries can still be pretty darn dissonant. Oftentimes, though, a little research will show that something cringe-worthy or laughable today is also something worthy of applause for what it stood for, and the context can be important in interpreting the work at large.
Authors often work under a system of rigid censorship that decrees even mild criticism of the status quo to be going too far, even in enlightened democracies. Attempting to argue for modern values would have really been pushing your luck. (In other words, here
Failure Was the Only Option.) A work that's only a
little culturally subversive is more likely to escape censorship and earn public acclaim than one that goes all the way, thus ensuring its relevance — or at least survival — into the present day. (For an ironic counterpoint, consider
Crosses the Line Twice, which is when one has to go all the way to get away with being
offensive.)
Please remember that this trope does not mean "surprisingly enlightened for its time period." It means "
more enlightened for its time period", which is not necessarily the same thing. If a vintage work has a message that comfortably fits modern audiences, that's
Values Resonance. To qualify for Fair For Its Day, a vintage work must have negative cultural traits as well as positive ones.