I would tend to imagine that the number of people who have never wasted some sperm in their lives is close to absolute 0.
So between that and no contraception, what's the difference?
If God gave us wet dreams, he gave us the right to waste sperm in little rubber containers. Or spray it all over the wall, for all he cares. I mean, it's a little hard to believe that God expects us to be chief financial officer for little dudes we create in the billions.
I would expect it is simply much more logical to assume those religious beliefs were codified in times where we really didn't have a clue how all the plumbing worked.
Between more effective methods of avoiding creating real world problems and assuming that those beliefs reflect the true will of God, I know which side I fall on. Pluck a person who's never been exposed to the teachings of the church, and they would have never ever even considered such a theological limitation. People get it from their churches, who got it from older folks, who got it from older folks ... there are some notions that, even if I accept the possibility of a theology, are far more likely simply to be a spiritual case of broken telephone.