I do believe we are as much a product of the choices we have made in favor of one or the other, as much as anything else.
This idea strikes me as Aristotelian rather than Kantian. (Although I'm not sure you were suggesting it was in fact Kantian?) Aristotle argues in the Nicomachean Ethics
that the more we habituate a life of virtue through making virtuous choices (or the converse), the likelier we are to make such choices in the future. He notes that "our character is determined by our choosing good or evil" (1112a). Eventually choices that are voluntary and deliberate become incorporated as traits and thereby lose their volitional nature: "Let us assume the case of a man who becomes ill voluntarily through living a dissolute life and disobeying doctors' orders. In the beginning, before he let his health slip away, he could have avoided becoming ill: but once you have thrown a stone and let it go, you can no longer recall it, even though the power to throw it was yours, for the initiative was within you. Similarly, since an unjust or self-indulgent man initially had the possibility not to become unjust or self-indulgent, he has acquired these traits voluntarily; but once he has acquired them it is no longer possible for him not to be what he is" (1114a). This makes perfect sense to being me, especially in terms of sin. The more we cultivate a life of sin, the less able we become to adjudicate between good and evil. Eventually through disuse the faculty of moral judgment atrophies and dies like any other organ. I've always been reminded of that bit in Canto XXXIII of the Inferno
where in Ptolomea Dante sees the sinner whose soul was taken to hell before his physical body died, a demon replacing the man's soul on earth.
It's been too long since I've read Kant for me to comment on exactly where he would differ from this. I'm inclined to think, however, that Kant would not agree that it's possible for us to lose our moral reason so completely as Aristotle suggests. Indeed, I think Kant would reject the notion that our previous moral choices determine in any way our present capacity for moral judgment. To admit our previous judgments into our present reasoning would on the Kantian view--at least I think--prevent our formulating a true categorical imperative. Ah well. Once again I may have completely misrepresented the Kantian position. If so, mea culpa
! I'm open to correction!
I only remember a small amount of Kant regarding Categorical Imperative. I do remember him talking about the morality, the good or evil of an action, being based firmly and solely on the intention of that action. I know the Church and many Catholics in general would disagree with that to some degree, but I agree with it, at least in part. The consequence of an action still has bearing on the morality of the action, but in my opinion, the intention is more important that the consequence or outcome.
Are people naturally inclined towards good or evil? Given the Church's teaching on Original Sin, I would say we are at least somewhat inclined towards evil and must work extremely hard to overcome that inclination. Do people intentionally say or do things to hurt others? Absolutely. Is that immoral? Absolutely. There is never a question as to the morality of gossip, backstabbing remarks, slander and so on. There is no question as to the morality of murder, abortion, stealing or any other sin against the commandments.
Kant states that the only absolute good is a good will. He says that a good will is the only thing that is unconditionally good.