I have to say, yes, we can forgive old movies. And sometimes, we should.
A most controversial one that we actually NEED to, like it or not, is Triumph of the Will. Yes, it's pro-Nazi, a regime subsequently found to be so heinous and foul as to become literally synonymous with evil. But it is also the precursor to virtually all modern film, and that is not hyperbole. Leni Riefenstahl's photography and cinematic techniques, experimented with in her previous films but perfected here, gave birth to the modern cinema.
If a film is simply a product of it's times, then let it be. Use it to tell our kids of how the world used to be. On the other hand, those films with no other purpose than to espouse outdated ideals? Let them sit in the archives and be footnotes for media students.