More on the image of God at Auster. The criticism is that any discussion of whether people might lose the image of God and/or become subhuman leads to concentration camps, more or less.
The slippery slope argument pretty much sums up all opposition to HBD. If you criticize a racial or ethnic group, or often any member of (certain) groups, you are essentially saying you want them killed/enslaved/treated inhumanely. It’s as dumb as a box of rocks, but combined with hysterical emotional intimidation it works very well.
A much bigger real problem is the doctrine of the divine spark or inner light. It’s a pagan idea from Greek philosophy, and had no social effect then- Plato and Marcus Aurelius didn’t believe in freedom for slaves or universal suffrage. Presented in the modern world as a Christian idea, it is one used to demand universal rights and power of the people, which ends up being the power of the few. It is also used to prevent needed restrictions on the population, such as discipline and control, because these are affronts to the dignity of the divine-natured individual.