Much like in the earlier episode "I Warn You Three Times," it seems that a witch's primary goal is to seduce men and then arrange for them to die.  It seems creepy because of the whole "black widow" theme.  But, let's say you had a terminal disease, and your only two choices were die WITH the best sex of your life or die WITHOUT the best sex of your life.  (However, that was not the plot here.)  Witchcraft.