There isnt much nutritional value in cheesecake.
This is true. Cheesecake is far from the healthiest food choice. But it’s still a food. Our bodies need fat, carbohydrates, vitamin A. I would agree that eating* only* cheesecake is not in accord with our nature, but eating cheesecake in and of itself does not violate our nature.
Eating cheesecake is for pure pleasure, not out of necessity.
“In accord with nature” does not mean only that which is necessary for survival. Sleeping seven or eight hours a night is in accord with our nature, even if a person could survive on less. Visiting with our friends and family is in accord with our nature, though we often do these things for pleasure, because we are social creatures. This is true even though some people prefer to remain solitary or choose to become hermits.
On the other hand, having sex with one’s spouse is in accord with our nature.
I agree; there’s no dispute there.
What I am wondering is how the Church comes to the conclusion that contraception is bad. My understanding is that their conclusion on this matter comes from fallible theologians, not from God.
The Church is guided by the Holy Spirit. It has taught that contraception is wrong for over 2000 years. The teaching
does come from God, it is just that God chose to reveal it to use through our nature and our reason, rather than through divine revelation.
You can find other examples of this. We know that child abuse is wrong, not because Jesus said, “Thou shall not abuse your offspring” but because we can reason that parents ought to love their children. We see that this is best for the children themselves, for society. We recognize that children who grow up in loving homes do better than children who grow up in abusive situations. In other words, we know instinctively and rationally that child abuse is wrong, even though we never read about it specifically in the Bible.