Denial of the validity of IQ is one of the main factors that justifies the biggest form of discrimination in existence: discrimination based on intelligence. I was born wealthy, and some people are born homeless, purely based on IQ. This is patently unfair, but you can't address that if IQ isn't real. I think people deny the validity of IQ because they are afraid if IQ is real then our society is structured in a way that is very unfair to people with low IQ.