When Charles Darwin developed his theory of evolution by natural selection, it didn't just change our awareness of biology, but our philosophy of reasoning. But since that time it has continued to cause controversy. Those who are aware of the factual basis of common descent and genetic development find it slightly preposterous that controversy continues, and outraged by parents who are obstinantly against the teaching of evolution in schools. I sympathize with them, but I am less outraged by the outrageous behavior of the "creationists" than I used to be, because I've learned to understand them, and their arguments, in a new light.
In essence, what they object to is the teaching to children that smart people should be ruthlessly self-interested robots who copulate with as many victims/partners as they can, willing or not, because replicating their genes is the only possible meaning or purpose to their existence, and anyone who thinks otherwise is fooling themselves because they're weak or stupid. Sure, they never spell it out in so many words, but it is the basic "zoological Copernican theory" of the modern message of atheistic evolution.