One of the biggest difficulties in understanding and acceptance of evolutionary biology is the eye. It isn't just detractors who are trying to protect a sectarian viewpoint, it is genuinely curious people, smart people, who don't get it because it isn't easy. Science is difficult and, inside science, evolution is difficult. We've even had prominent biologists here submit the idea that perhaps, given its difficulty, evolution might be better reserved for college students, the same way quantum mechanics is reserved in physics and surgery is reserved for actual doctors even though high school students learn anatomy.