Chex:
My theological discussions with Protestants on this matter rarely involve the Bible.
To this, they say, “…so…” and proceed to point out that the Bible says nothing against it.
Really? So on what basis ( if the bible says nothing) did all, I repeat ALL, of the Protestant churches consider contraception a vile sin for over 400 years? Did they just make it up or was that their interpretation of Scripture? It was their interpretation of Scripture, of course, and the witness of the entire Christian community for almost 2000 years. They simply caved in to society at the 1930 Lambeth Conference. Plain and simple.
Chex:
I attempted to point out that section in Gensis where God killed a man for “spilling his semen” before intercourse, but the circumstances make it an admittedly weak arguement.
One can say that it is relatively weak compared to other explicit teachings, but compared to THEIR argument it is very strong. They have nothing. Here is the biblical reality: Onan was killed for “spilling his seed”. Protestants will likely say that he was killed for not fulfilling his obligation to bear a child for his deceased brother’s wife. Unfortunately for them, the penalty for failing to meet that responsibility was NOT DEATH, it was public humiliation. So why was Onan killed? For spilling his seed. Even if that were the only mention of it in the bible that should be enough. You need to read all of this:
catholic.com/library/Birth_Control.asp
Here are a couple of exercpts from that tract the 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.)
Does it sound like these men were unsure of their biblical interpretations? Who’s kidding whom? For almost 2000 years ALL CHRISTIANS were of ONE MIND regarding contraception. God has not changed, the bible has not changed, the Catholic Church’s teaching has not changed; only the interpretations of those people unauthorized to interpret the bible have changed.
Chex:
I read Humanus Vitae and other encyclicals and article on this site, but found little besides more ethical points of view. So I was wondering if anyone has any (clear) scripture which I can add to my side of this debate.
You already have it in Genesis - is it not clear enough when the topic is a man avoiding impregnating a woman by intentionally interrupting sexual intercourse? What would be more specific than that? And if there is nothing else, then you have to go by WHAT THERE IS, not by what you wish were there.
While ethics can be debated, the Bible is infalliable.
Thanks!

I thought you were Catholic. Ethics can be debated? You don’t understand what the Church is. You need to do some basic review.
The bible is not infallible, its inerrant. If you didn’t know that, you probably are not in a position to understand Humanae Vitae or other encyclicals without assisstance. That is what the Church is for.
Let me know if I can help…
Phil