I believe that Charles Manson quotes are too controversial for writing prompts in an English class. He was the leader of a cult, who led the members of the cult to commit horrendous murders. Charles Manson and his quotes are inappropriate to present in a classroom environment as a writing prompt. I personally believe his words do not deserve to be celebrated.
No, quotes by Charles Manson are not to controversial to use for English class. Charles Manson is an import figure in United States history, and the students of this country need to learn who he was, and what he did, and maybe it will prevent this from ever happening again.
That depends on the context of those writing prompts. But I think that if you're asking this question, then you probably don't understand the depth behind that quote, and you probably should not be using it at all. Words have power. Choosing words from an unstable murderer can probably give your words power you don't intend.
Charles Manson quotes aren't too controversial for writing prompts in an English class. William Shakespeare, Benjamin Franklin, George Washington and Winston Churchill were controversial in their societies and their quotes are used for writing prompts all the time. Manson is controversial due to the murders he and his "family" committed. His quotes are so controversial as the man himself.
I suppose if someone found a Charles Manson quote interesting it could be used as a prompt for writing in English class, but my question would have to center around why you would want to write based on this persons quotes. I suppose its not controversial and people can find inspiration in many things, however I would chose someone else personally.