[Diddle E. Squat]

f God gave you a birth control device as part of your anatomy, there would be no difference. The God-given method of birth control is knowledge of fertility cycles and abstinence. If you use these, you use your body as intended. If you divert, block, or render infertile the sperm, you pervert the sexual act to exclude (1) God, who is a partner in the procreative aspect of the marital act; (2) Your spouse, who is no longer fully engaged in the unitive aspect of the marital act.

Well, God didn't give us pacemakers as part of our anatomy, is that also sinful and a perversion of the God-given heartbeat? For that matter, he also didn't give us stomach feeding tubes, so is it sinful to insert one into a person's belly?

[Tax-chick]

A heart attack is a bad thing. Starvation is a bad thing. Avoiding those outcomes (by any moral means) is good. A child is a good thing. Avoiding that outcome, even by morally-acceptable means, requires a strong reason.

[annalex]

God didn't give us pacemakers

The difference is that in order to heal an illness, to use an artificial device is ethical. If your intent is to defeat the healthy operation of your body, you cannot use anything that is not inherent to that very operation.

Is it too abstract? Your body is made to procreate, and the female body is made to be periodically infertile, and is has a brain to count days, take temperature, etc. It is OK to follow the way God designed the body toward an otherwise moral goal.