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."What changed in 1930?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.)
As to that, I don't know.
As to the rest, I'm constantly grateful that my conscience is captive to the Word of God -- and not to repeat the mistakes of others.