Personally, I think every parent has the right to object to subject matter being taught in their child's school. However, taking books off library shelves censors for everyone, not just one's own child. When it comes to required reading, a reasonable alternative is to have a list of alternate books for children whose parents object to content, or to allow the parents to propose an alternate book of their own that's reading-level-appropriate.
The map above is created by bannedbooksweek.org to illustrate cases of book bans and challenges from 2007 to 2009 in the United States.
I'm going to find a banned book to read.