NFP Or A Full Quiver?

I've been looking for more sites discussing the theology and the reasoning behind Natural Family Planning or NFP over birth control or the Quiverfull ideology. I believe deeply that there is a difference between actively sterilizing a fertile act of marriage, as opposed to simply not engaging in a fertile act of marriage. And I respect the deep faith of the Quiverfull families, though I do resent some Quiverfull families idea that NFP is the same as the pill.

Many sites that I have found discuss the sin of Onan. In one page I was promised discussion on the topic of birth control from Luther & Calvin. With my many reformed friends, I thought that would be great. But here is what I found:

Quoting from this site:

The apostolic tradition's condemnation of contraception is so great that it was followed by Protestants until 1930 and was upheld by all key Protestant Reformers. Martin Luther said, "[T]he exceedingly foul deed of Onan, the basest of wretches . . . is a most disgraceful sin. It is far more atrocious than incest and adultery. We call it unchastity, yes, a sodomitic sin. For Onan goes in to her; that is, he lies with her and copulates, and when it comes to the point of insemination, spills the semen, lest the woman conceive. Surely at such a time the order of nature established by God in procreation should be followed. Accordingly, it was a most disgraceful crime. . . . Consequently, he deserved to be killed by God. He committed an evil deed. Therefore, God punished him." John Calvin said, "The voluntary spilling of semen outside of intercourse between man and woman is a monstrous thing. Deliberately to withdraw from coitus in order that semen may fall on the ground is doubly monstrous. For this is to extinguish the hope of the race and to kill before he is born the hoped-for offspring." John Wesley warned, "Those sins that dishonor the body are very displeasing to God, and the evidence of vile affections. Observe, the thing which he [Onan] did displeased the Lord-and it is to be feared; thousands, especially of single persons, by this very thing, still displease the Lord, and destroy their own souls." (These passages are quoted in Charles D. Provan, The Bible and Birth Control, which contains many quotes by historic Protestant figures who recognize contraception's evils.)

From my understanding, Onan's sin is deliberately shirking his duty to his widowed sister-in-law, with whom, by order of Jewish law, he should bear a son to carry on the name of his deceased brother. While his sin is manifested by the "spilling" of "his seed", I am not wholly convinced that it in itself is the sin of Onan.

The Quiverfull mentality is lovely. But I also believe that God has given us this wonderful intellect for a reason, which is not to say that Quiverfull families don't use their intellect. But for some women it is downright dangerous to get pregnant. And such a woman should not feel forced to procreate simply to be a Christian. I'm not accusing all Quiverfull's of this attitude, only some.

NFP is such a complex issue, and with it comes such depth in the marital relationship. Intimacy is redefined (from our current cultural definition), and explored. Women's bodies are kept free of harmful chemicals. Newly conceived children are not put in danger. Families can be spaced without losing the deep respect for human life and it's potential. And the marital act is never truly separated from it's functional ability to create children. I believe God gave us sex within marriage for multiple reasons, and to, as a society, decide that it is only for pleasure and procreation simply a nasty side effect, is to decrease it's meaning and value. NFP has so many benefits, I feel blessed to be able to use it.