I was raised agnostic/atheist so obviously I didn't have an issue with teaching the theory of evolution. The teacher who supervised me during my student teaching was Christian. I knew that he covered evolution and I asked him how he reconciled it with his religious beliefs.
He said (paraphrasing) that it CONFIRMED his belief in God because it was a perfect plan. He said God wouldn't design living things to suffer and die for generations as their environment changed. Instead, God designed a system where the fittest survive and thrive and those that were not the fit mercifully died and didn't get to pass their genes onto the next generation.
To me, a big part of the issue are the believers who take 100% of the King James version of the Bible as the literal truth. Of course, that's ludicrous, because the Bible wasn't written in English. It was written in Hebrew, Aramaic and Greek. Furthermore, it was written in ANCIENT forms of those languages and translated over a thousand years later. How can a translation of a translation many times over be the "inerrant word of God"?