Eh, I think its less simple than that. These old things continue to exert their power. Its true that they fade with time, but if we put a label on it and say "see, this is racist (or whatever)" then we've put a marker in the sand and that is not nothing. I don't think we're being asked to go out and find copies and burn them, or actively vilify the authors, who may well have learned, changed, and grown and could be quite praise-worthy people.
I mean, sure, we should be careful about handling 'facts' that are merely posted onto a thread, they could be less than perfectly accurate, and probably ARE at least slightly biased. OTOH I think this one is a pretty clear case where we can at least safely say "As depicted, this is not good stuff." I am with you though in having refrained from any kind of more detailed commentary on the specific subject matter, since I never read it. I am willing to accept however that it is bad, and what I saw was not good. Some posters got into a pretty decent amount of detail too, which makes me less suspicious of misrepresentation.