Nor is it particularly Christian... in fact other religions that are un-Christian have the same reasoning... manicheasim (sp?) as well as neo-platonism. Pelagius was rejected, in great part, because Augustine was a Bishop while Pelagius was a simple monk. Then, as now, politics was a God to a lot of church folk.
Ask any 100 Christians and I am sure at least 99 will say Jesus
repaired the breach caused by Adam's disobedience. There is nothing weak-willed, mortal little 'ol me can do to repair it any further. As a mortal, I simply cannot effect it anymore than the sacrifice of God on Earth, though this is just IMHO.
I'm sorry, I thought the post was just about homosexuality... not smoking, though it applies to that as well
The Maniches and the neo-platonists, among others, had a similar idea, but it is not the same when you look at it with a little care. In those cases, the idea was that matter itself was to blame for our human weakness, that we are pure souls imprisoned in flesh, and that the goal of a human being was to overcome the effects of this by various sorts of purification. After death one was freed permanently or temporarily from this imprisonment, depending on the teaching of the group in question. (You can see a similar POV today in Hinduism.)
This view was popular both at the philosophical and popular level for a few reasons, including the philosophical understanding of matter as changeable and corrupted and the immaterial realm as the source of stability and truth, and the general human experience of intending or wanting to do something and then finding oneself doing the opposite.
The difference comes because of the insight that Christianity has from its Hebrew roots - that matter is not separate from God, evil, and the source of corruption, but rather that it is created by God and is good according to the nature God gave it.
But this leaves open the question of why we are then not able to reach God by our own efforts at goodness, and why we perceive a separation from him. The Christian answer to this has been the Fall - human (and angelic) free-will, and the effects of choosing untruth over truth. It is not, as in the neoplatonic view, an explanation that sees the origins of the problem in matter, but from the soul, though that affects matter. In humans, the effects of the Fall are understood to be passed through the material.
Yes, you are right that Christianity teaches that Christ healed this chasm between us and God, but that is not a complete statement. If 99 out of 100 Christians say so and nothing more they haven't thought very hard about it, or bothered to read much theology. Clearly, we still all feel its effects. I am not sure how you could possibly understand it otherwise, unless you expect to see people, as Pelagius claimed they could, simply and successfully choosing not to sin so long as they tried hard enough, or at least finding that to be the case after baptism. You seem to understand that is not the case with smokers, which makes your claim that concupiscence cannot be part of the issue with other things like homosexuality, because concupiscence doesn't exist, a bit suspect. If you are right that "God doesn't make junk" in the way you claim, than there should not be anyone who really wants to who fails to quit smoking.
I'd be interested to know, if you take the viewpoint of Pelagius, how you explain this.