Do you mean that for you the two words Missionary and Position put together don't carry any sexual meaning? Then let me explain it to you: The Missionary Position is the name of one of the many possible position both partners can use during sexual intercourse, specifically the one where the girl lies down on her back and the boy lies over the girl.

If you didn't know that, I understand that you might not see the sexual connotations of such a title. But please don't tell me Hitchens didn't know, it would be the most formidable misunderstanding in the history of debating.