As another English major, I'm disappointed that I haven't read more of these books by my own choice, but I aim to remedy that.
Growing up, my mother was an educator, and never censored me from reading whatever I wanted to read. She figured all reading was beneficial, at least as a work-out for the mind, and she trusted me not to read "Mein Kampf" and actually buy in to it.
And I aim to raise my kids the same way. It angers me that people do this, mostly out of ignorance. The best defense any parents can have against offensive material is to be well-read themselves, and to know precisely what it is they want to shield their child from, but nobody should have to suffer because of your ignorance.
On a lighter note, the funny/cool thing about Shel Silverstein being on that list is that he actually has written some stuff people might find really objectionable, although it's not that title, he wrote a series of short plays titled
An Adult Evening of Shel Silverstein. One of the plays consists of a man and a woman listing off euphemisms for the penis and the breasts. It's hilarious, (not, I believe ban-worthy, although I don't believe anything is) but not exactly something the average child reader should look in to, nor should a high school student (within the confines of the class, at least) seeing as it's all shock-factor and really lacks much poetic value.