In the sixties many leftists tried to spread the lie of the tabula rasa or blank slate. You were only what society had stuffed into your head. That myth has been thoroughly debunked. Humans are hardwired for many things including intelligence. If there is no such thing as IQ or meaningful intelligence tests, I could then examine the IQs of scientists, doctors, lawyers, mathematicians, engineers, architects, etal and find a lot of average or sub-average IQs. I don’t think I’d find that.
The "tabula rasa" theory is the basis of free enterprise and personal liberty. It implies that anyone has the potential to rise above their circumstances through effort.
IQ is considered determinative, which makes it a convenient tool for nanny-state authoritarians to maintain their power over everyone else.