Why Sarah Palin?

I've thought and thought about why McCain picked Sarah Palin. Sarah Palin, a charismatic woman who has not demonstrated any thinking on the big foreign policy or economic issues of our time, is for teaching creationism in the schools, opposes abortion, even in cases of rape or incest, who wanted to ban books... Sarah Palin does not appeal to the broad middle; her appeal is almost solely to the far right of the Republican Party. Her acceptance speech threw red meat to the base and did not even try to reach out to the middle. Why would the campaign reach out almost exclusively to the far right when conventional wisdom is that the only way for McCain to win this race is to appeal to independents and Reagan Democrats? Could it be that the McCain campaign believes it needs to appeal only to the base on the theory that the base when added to the number of voters that will never vote for a Obama, no matter what the McCain campaign stands for, throws McCain over the top? If he were to win with that strategy - appealing to 25-30% of the voters, how would he govern?