Low-church leftists believe that if IQ is real, it justifies killing anyone with a low IQ. This is a very stupid idea for myriad reasons, but exactly predicts the behaviour you see in the field.
"If IQ is real, killing every Bantu is okay!"
"If IQ is real killing me is okay!"
No wonder they don't like being reminded that IQ is scientifically unassailable. "Something something math is racist." It's just part of their religion.
If they really were vaguely rational, you could get them to submit to IQ by first attacking and discrediting the arguments that show IQ => eugenics. Of course, you can't reason someone out of beliefs they weren't reasoned into. Sometimes you can socially bludgeon them. Act high status and slyly signal that anyone believing IQ => eugenics is low status. Of course, even if they were vaguely rational, you would have to first use extreme empathy to even discover that the arguments exist, since they categorically refuse to talk about it. Have to read a whole ton of their writing and sew together all the hintful scraps they accidentally drop.
Why bother with all that? Belief flows from the barrel of a gun. Replace their Pope and they'll turn on a dime, as per Havel's Greengrocer. They barely understand the beliefs anyway. It's largely ritualized verbalization based on animalistic, Pavlovian triggers. The ideas are above their station and it would be best if they were liberated from having any opinions at all about them.