1. IQ is one of the most heritable psychological traits – that is, individual differences in IQ are strongly associated with individual differences in genes (at least in fairly typical modern environments). www18.homepage.villanova.edu/diego.fernande…
(Note that the Flynn effect shows that IQ isn't 100% genetic; it doesn't show that it's 100% environmental.)
If IQ isn't a valid concept, no concept in psychology is valid.
Conversely, IQ-denial could cause real harm by stalling the development of such interventions.