I think that what it all comes down to with us beings, is that we often have our own upbringing that influences how we believe. This is called socialization. It happens to every being when they are growing up. There are many factors that contribute to this such as country, county, city, churches, parents, brothers and sisters, friends, community members, political parties, diversity, everything. Some people are brought up to believe that it is ok to date/marry anyone you like, regardless of color and regardless or religious tradition. My family was like this and that is why I am the person that I am today. Not to defend Kasey, but I have to almost feel sorry for him because of his socialization which led him to be this way. He may have grown up in an area of the world that does not have much diversity and so to see two people "mixing" with others, it might seem strange and even wrong. So when he became a Christian, he tried to find verses in the bible that 'might' help him feel better about what he was seeing.
I did this too when I was a Christian to a certain extent. My heart was very liberal so to speak but my communty was not. So I spent time trying to find scripture that refuked what was being taught. Needless to say, we all are guilty at one point in our lives for taking something that has some truth, and changing the way that it means to us creating a new truth. It all is just a misconception of reality. We have taken reality and changed it to become a new reality that fits into our world views.