Isaac Hayes is undoubtedly a great musician. He is however a member of the controversial Scientology cult. The "World Literacy Campaign" also promoted by Isaac Hayes is a Scientology front group. (Scientology has many such groups.)
You can read about Scientology and it's nasty secrets on the internet at sites such as:
http://www.xenu.net http://www.scientology-kills.net
"Scientology is evil; its techniques are evil" - Victorian Supreme Court