It was years after I'd left the evangelical church that I realised that the whole "no sex in heaven" thing was based on the one saying of Jesus that people in heaven would "neither marry nor be given in marriage; they will be like the angels in heaven". But Genesis (and in the NT, Jude) has stories about angels coming down from heaven and fucking human women, and so where would we get the idea that "being like the angels in heaven" doesn't mean "unable (or indeed unwilling) to fuck"? I think a far more responsible interpretation would have been "People in heaven have lots of sex, without caring about who they're married to". I can't think why the evangelicals don't preach this more. :)