Martin Luther and John Calvin are recognized as fathers of the Reformation.
Martin Luther (1483 to 1546) - "Onan must have been a malicious and incorrigible scoundrel. This is a most disgraceful sin. It is far more atrocious than incest or adultery. We call it unchastity, yes, a Sodomitic sin. For Onan goes into 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."
John Calvin (1509 to 1564) - Deliberately avoiding the intercourse, so that the seed drops on the ground, is double horrible. For this means that one quenches the hope of his family, and kills the son, which could be expected, before he is born. This wickedness is now as severely as is possible condemned by the Spirit, through Moses, that Onan, as it were, through a violent and untimely birth, tore away the seed of his brother out the womb, and as cruel as shamefully has thrown on the earth. Moreover he thus has, as much as was in his power, tried to destroy a part of the human race.
Also, John Wesley is recognized as the founder of the Methodism.
John Wesley (1703 to 1791) - "Onan, though he consented to marry the widow, yet to the great abuse of his own body, of the wife he had married and the memory of his brother that was gone, refused to raise up seed unto the brother. Those sins that dishonour the body are very displeasing to God, and the evidence of vile affections. Observe, the thing which he did displeased the Lord - And it is to be feared, thousands, especially single persons, by this very thing, still displease the Lord, and destroy their own souls.
Examining sermons and commentaries, Charles Provan identified over a hundred Protestant leaders (Lutheran, Calvinist, Reformed, Methodist, Presbyterian, Anglican, Evangelical, Nonconformist, Baptist, Puritan, Pilgrim) living before the twentieth century condemning non- procreative sex. Did he find the opposing argument was also represented? Mr. Provan stated, "We will go one better, and state that we have found not one orthodox theologian to defend Birth Control before the 1900's. NOT ONE! On the other hand, we have found that many highly regarded Protestant theologians were enthusiastically opposed to it."
Here are several previous threads on the subject:
And people wonder why so many modern young people have fallen away from the Bible’s teachings? Onan pulling out is supposed to be worse than adultery? Worse even than incest?
The human male makes and discards ~200 million sperm per day, and yet Onan pulling out is supposed to be akin to killing a son before he is born?
Order of God in procreation? Honestly. How can anyone escape the conclusion that these writers were railing against a reproductive system they did not fully understand?