I applaud the action taken in putting up the disclaimers. If only to end this (IMO) incredibly stupid debate.
I am reminded of going to Los Angeles more than a decade ago, and seeing, for the first time, labels on almost every thing (including buildings) informing me that they might cause cancer. As well-intentioned as those labels were, the initial shock quickly turned into a lack of caring. If everything is labeled as possibly causing cancer, then, well, who cares about the relative risks of anything, right? This is roughly the equivalent of slapping labels on all films saying that they might depict sexuality or violence, such that Salo, or the 120 Days of Sodom is labeled the same way as The Muppets Take Manhattan.
It is an unfortunate and banal truism that all products are reflections of their time. If you buy something from 1850, or 1985, it is unlikely to reflect everything we expect today; in much the same way that if you bought a car from 1950 that had not been changed in any way, it wouldn't meet current concerns regarding pollution controls.
Merchant of Venice does not reflect appropriate concerns regarding anti-semitism, and Romeo and Juliet does not reflect age-appropriate romance. Gilbert & Sullivan is not exactly culturally sensitive (and I can't imagine what Mr. Kwan would make of The Mikado; I would assume that's at least 5000 tweets and 10,000 hours of Youtube). Stanley Kubrick spent his career as a filmmaker pretty much ignoring LGBTQ roles and representation, as did almost all directors from the dawn of Hollywood through, well, today.
Yes, old books reflect their time. They should probably be labeled as books as well. Again, to the extent this will stop people from complaining on twitter about it,* it's a good thing I guess.
*It's twitter; people will find a new and even more annoying thing tomorrow, if they haven't already.