A severe morality holds that intercourse (and may hold this of eating, too) has something wrong about it if it is ever done except explicitly as being required for that preservation of human life which is what makes intercourse a good kind of action. But this involves thoroughly faulty moral psychology. God gave us our physical appetite, and its arousal without our calculation is part of the working of our sort of life. Given moderation and right circumstances, acts prompted by inclination can be taken in a general way to accomplish what makes them good in kind and there's no need for them to be individually necessary or useful for the end that makes them good kinds of action. Intercourse is a normal part of married life through the whole life of the partners in a marriage and is normally engaged in without any distinct purpose other than to have it, just as such a part of married life.