Why are Creationism and Evolution such controversial topics in the U.S. today ?
Because Americans, culturally, have a distrust of the conclusions of authorities, particularly intellectual authorities. We love it when our moms turn out to have been right all along. We never believe the government when it tells us it knows what's best. We love to root for the underdog.
Well, creationists, hampered as they are by a lack of scientific credentials, a lack of rigorous reasoning, and a lack of good evidence, are certainly the underdogs. It's no surprise that creationism as a means of "sticking it" to those know-it-all scientists would appeal to the significant portion of the population that view themselves as Davids to various Goliaths, as well.
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