Another thing, is why do those angels have to be bad? I think maybe most were good ones. What's wrong with sex and marriage and children?
Well, look at it this way. There are only two kinds of angels, the kind that rebelled against God and followed Lucifer/Satan, otherwise known as fallen angels, and the kind that remained true to God and serve Him constantly. The second kind are not going to be fooling around with earthlings. Edit: They are supposed to be protectors of and ministers to human beings who are saved.