Ah yes, the slipper slope. Let's be honest, librarians and educators have a ton of power and no oversight in indoctrinating children into the views that they want. Now that parents are challenging them, all of sudden, PEN America believes that parents should have no say on the material their kids read.
It's not a slippery slope. That is literally what you are advocating. The same parents who don't want their children to know what Ruby Bridges went through or that gay people exist also don't want their children to learn about evolution.