That's how things go. Something comes out and it is unique, original, important, timely, thought provoking. 40 years later it may not be any of those things (in one mans opinion), but it can still be appreciated for what it represented when it was made.
Despite what you may think of the "moral" of the film today, that has no impact on the fact that it is still a quality film regardless of the calendar.
Much like the soundtrack for Cool Hand Luke. I think most of the movie stands the test of time, but the soundtrack isn't good.