Matt 5:
27"You have heard that it was said, 'Do not commit adultery.'[e] 28But I tell you that anyone who looks at a woman lustfully has already committed adultery with her in his heart. 29If your right eye causes you to sin, gouge it out and throw it away. It is better for you to lose one part of your body than for your whole body to be thrown into hell. 30And if your right hand causes you to sin, cut it off and throw it away. It is better for you to lose one part of your body than for your whole body to go into hell.
Every religious rule or prohibition regarding human reproduction has one goal in mind- To make more believers.
No birth control, no abortion, etc. ALL seek to control people's behavior so that they reproduce more, thus resulting in more offspring who are likely to grow up with the same religion. More believers=More power, more money.
Funny how somebody placed a link with a scientific study supporting masturbation as a harmless habit, so I'll do my share too, though with one saying more or less the opposite of the first. This says excessive sex drive might give men prostate cancer:
http://news.bbc.co.uk/2/hi/health/7850666.stm