What is the obsession people have with quote mining?

I see a lot of people do this. Picking out quotes in order to make themselves look correct. Christians do it when preaching the Bible, creationists quote mine(and, out of context) when trying to disprove evolution, and people do it left and right in political debates, particularly in the US. Why do people quote mine so much? More importantly, how does quote mining actually make someone the correct one in an argument?