Here's another interesting panel discussion from
Chicon 8.
Sometimes works that were once popular don't age well. It can be elements that are now dated -- a major part of the plot hangs on a character being able to find a payphone, or a character dies dramatically of something that is easily curable today, etc. But all too often, something is handled in a way that makes us cringe when we're supposed to be having some other emotional response. Or we learn something about the author's personal life that we find cringeworthy, if not outright repugnant.
The first can often be an example of "the past is another country; they do things differently then." It is one of the ways we often come up against the linguistic principle that writing is "frozen speech." A person recalling a personal experience from decades earlier might tell the story differently now, perhaps soft-pedaling awkward aspects of how things were done back then. But the story that is written continues to present itself to new audiences in its original form, showing the attitudes and practices of days gone by.
Sometimes editors have tried to touch up older works to bring them in line with modern sensibilities -- but while some readers may have welcomed the changes, the most vocal critics were those who decried it as bowdlerization, as fandom saw some years back when Eric Flint removed some references to smoking and other dated things from some of the stories of James H. Schmitz and aroused a furor.
The other problem is more difficult to deal with. Sometimes it too is a situation of "the past is another country: they do things differently then." What was unremarkable, even normative a century or two ago can arouse disgust now. But when we're dealing with authors who were active in our own lifetimes, or if things coming out about them are way beyond the pale, even in their own times, we have to do some serious thinking about how we judge the work in relation to the author. If the book is still in copyright, there can be the consideration of our money going to these people or the people who enabled them. But even if the work is out of copyright, we may have some thinking to do about the problem of good (or even great) art created by bad people. Sometimes the bad leaks into their writing in subtle ways that can affect the reader's attitudes. However, one must also consider that, if we restrict ourselves to only reading books by authors who are known to have led exemplary lives, we could soon find ourselves on very short literary rations.