Lies beget lies...
You should question ANY ideas of any of the Church fathers. IF any of their ideas were pulled out of thin air, then they would have to invent new stuff to cover up the holes it creates when scrutinized. And finally the corruption is complete and the religion is not savable or recognizable for what it originally was.
You should do reversible engineering techniques on these dogma. Take the immaculate conception. You should ask - why did Mary need to be sinless from birth? Is there really a need? No... then why did one establish such? ... you need to look at the influx of Manichaeism and monasticsim which were in their introduction merely extremists much like the ones we entertain today. As found with today's extremists - the lack of faith in established religion leads them to do "extra" things to be more worthy but doesn't see that they are moving outside the requirements and are in fact being counter productive regarding their own religion's guidelines for salvation.
And that is how new dogma is established... the need for extra - and the stretching of rules and boundaries. This is what started to happen as soon as the apostles were removed and the gnostic worms started to emerge from the woodwork. Gnosticism is the claim of having the esoteric knowledge of the teachings of Christ during his 40 day ministry as a resurrected being, having received the full Glory of His Father and therefore shared a oneness in purpose, power and knowledge with the Almighty. Only the Apostles knew the full extent of this teaching, but the Gnostics claims to have this knowledge.
Is copulation a sin? No... Why? Because it was the very first commandment of the Almighty to his creation. Even before Adam and Eve was taught about the tree of knowledge of good and evil, they received the commandment of going forth to multiply. Which is basically God saying to mankind. Go forth and have sex. How can an explicit commandment when followed be sinful? And the very first commandment given as well, which should indicate some sort of importance. There is no original sin... no hereditary sin. There is no sin passed on from father to children - hence there is no need for a immaculate conception. All are born sinless. Hence - child baptisms are not necessary. But children as all mortals born, needs resurrection - which is where Christ's grace will apply, as it will with Mary his mother.
Baptism - is for the remission of sins which will apply for those accountable. Commandments are not followed, laws are broken and Christ's mercy will save and mend.
So... if you do not copulate to beget children, you are sinning against the very first commandment given. Spinster nuns, monks and priests that do not multiply - are under condemnation, and will need Christ's grace to save them. As Luther realized...

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