You rightly assert that contraception that prevents conception is morally different than contraception that prevents implantation or that causes abortion. But even though it is less immoral to prevent life from beginning than to destroy it after it has begun, is it moral?
Consider:
3 Lo, children are an heritage of the LORD: and the fruit of the womb is his reward.
4 As arrows are in the hand of a mighty man; so are children of the youth.
5 Happy is the man that hath his quiver full of them: they shall not be ashamed, but they shall speak with the enemies in the gate.
Psalm 127:3-6 KJV
How moral is it to, in essence, say to God, "Uh, thanks, but no thanks. I mean, don't get me wrong; it's a nice reward, and all but, uhh, You keep it"?
The man of faith affirms that God is faithful and seeks to know His counsel in all things and humbly yield to His perfect will. Is it not hypocrisy, then, for this man to second-guess the Almighty regarding the bearing of children? Is this not -- sin?
Certainly it is sin. This is no less than the sin of unbelief; a lack of trust in God to do what is right: "God, we don't think You'd do this like we want it done so, if You'll excuse us Lord, we'll just handle this issue ourselves." One may as well say plainly, "God, I do not trust You with this one."
This kind of "I trust you with this but not with that" thinking works with people; we do it all the time. We assume that a 10-year-old can be trusted with sharp scissors, but they're not ready to be trusted with the family car. That assessment is perfectly fine, but it is entirely inappropriate -- blasphemous, actually -- to make the mistake of applying this kind of selective trust to God, because doing so makes the silent assertion that God somehow can't deal with the issue at hand; that He isn't really Who He says He is.
So, yes, it is less immoral to prevent a pregnancy than to abort one, but don't break your arm patting yourself on the back over it.
I can understand your point of view. Of course, one need not stop there. If you have the urge to have sex, in the bonds of marriage, but do not do so, is that immoral too? Is it immoral not to be married in the first place, never to have children? Some faiths do not allow their clergy to marry. Is this not denying God? One can go on and on along these lines of thought. So, I think it is a distinct moral difference that is something worth patting oneself on the back over.