I see the problem with public libraries as being the “tumah” that one is inevitably exposed to in both sights and sounds. I think that one should always try to avoid being in places where they will see or hear things that are inappropriate. This can apply to any not-Frum location, whether it’s a clothing store or a pharmacy, or grocery store. That is why I think that all of those places should be avoided if/when possible.
Obviously, each person has to make his own decisions when it comes to these things, and there are many factors involved, including the person’s level of sensitivity, how bad the particular place is, the person’s needs, and the alternatives available. Each person has to think things through and make his own decision regarding his actions.
But regardless of my particular choices that are based on my thinking things through, I can still acknowledge the fact that there is a level of sensitivity at which one considers entering a place that has any inappropriate sights or sounds similar to eating an apple from a toilet bowl. I might not be at that level, or I may have a need that takes priority, but I can still acknowledge that the level of sensitivity exists, even if I’m either not holding by it or it’s impractical for me.
So the way I understand the quote, it is not being holier-than-thou and an attempt to stifle independent thought. And I think that anyone who is confident in his decision-making process need not look at it that way.
btw, this is being typed up in a public library. And yes, I thought about it first. And yes, I do try to avoid the library when I can. And it doesn’t bother me that I am doing something that was compared to eating apples from the toilet.