Well, the following is how Mark Twain explained it:
In my schoolboy days, I had no aversion to slavery. I was not aware there was something wrong about it. No one arraigned in my hearing. The local papers said nothing wrong against it. The local pulpit taught us that God approved it and that it was a holy thing, and that the doubter need only look in the bible if he wished to settle his mind. Then the texts were aloud to us to make the matter sure. And if the slaves had an aversion to slavery, they were wise and said nothing.