I could not agree more and would not even do this to my own books. Ballpoint pens are not tools for marking books, and felt-tip highlighters should be prohibited altogether. Yet, students seem not to be able to do without them. In fact, they seem to think that their understanding of texts is enhanced by using different colors to indicate different categories. No serious reader will do this.
Needless to say, I don't own highlighters.
No further comment!
1. Needless to say, this episode has great significance in the novel.
2. See also here, here, and especially here.