The point is not about morals, but about the process of “ensoulment” itself.
You said sexual intercourse is a human participation in the process of creation. Agreed. However, the humans have little control over the process of the individual being “created” after fertilisation, which is the point, after all, that theists believe to mark the beginning of life. However, what I described is performed after fertilisation- the union of the sex cells had resulted in one individual, which, upto the blastocyst stage can be cleaved to create multiple individuals- and when this is done by direct human intervention, what should have originally been one individual, becomes many individuals.
If you claim this is some god’s plan, then you cannot say that doing this is immoral, because then it would imply that the same god’s plan was immoral, whatever that should mean.
God is outside time. Although we may frustrate His plan, He already knew before time began that we would do so, and He planned for it. We still have free will, because that enables us to freely choose to love Him (which is what He desires). God allows evil to happen, as a result of the free choices of men and angels, so that greater good may come from it. I’m not sure if that answers all your points.