Not every religion has to have St. Augustine's attitude to sex. Why even in our culture marriages are celebrated in a church, everyone present knows what is going to happen that night, but that doesn't prevent it being a religious ceremony.
We have got onto slippery ice where there is no friction and so in a certain sense the conditions are ideal, but also, just because of that, we are unable to walk. We want to walk so we need friction. Back to the rough ground!