It was really meant as a rhetorical question. The sin is in dismembering God’s gift of sex into two separate parts of unity & procreation. I’m not any kind of a theologian; there are far better ones right here on FR (and I’m pinging one) so I understand things as analogies (the simpler the better). If someone gives you an Armani suit, you don’t say, keep the pants, I just want the jacket.
That’s why IVF is as sinful as contraception, and why I was so concerned to find a Catholic OB/GYN who would at least understand my position, even if she didn’t agree with it.
The "wrong" of contraception is that the good gift of maritalsexual union is deliberately twisted apart or altered in order to contradict or deny one of the two God-given "ends" of marital sexual union, these two ends being Love and Life. Any act that intentionally undermines or destroys one of those ends, is by definition perverted.
That's why it is wrong to engage, even in marriage, in any act that is deliberately degrading, un-loving, perverted, or intentionally closed-off to the transmission of life. If you try to split off Life from Love or Love from Life, you are dismembering an act which was created, by God's design, to graciously revere and respect both.
It's like taking to that Armani suit with a scissors, and cutting out the butt of the pants. It would not only harm the design, it would insult the designer. Or, in the case of married love, the (capital D) Designer.
If you have an extra few minutes to read something which may make more sense of this, I invite you to try This Article (Link).
Blessings on uou!