Man could previously reproduce in an angelic manner; after the Fall, he relied on this carnal manner of procreation, suitable for the irrational animals. That can hardly be regarded as a neutral change. Sexuality therefore can only be seen as a mark of corruption. That isn't to say that sex, in its proper (married) context is bad, but obviously it isn't holy or ideal either.
This is the way I had come to understand the patristic tradition as well.
The marriage bed is undefiled, but that still has qualifications attached. For example, "undefiled" isn't necessarily a free license for sodomy in marriage. Many an Evangelical Protestant sermon I heard over the years encouraged teenagers to be sexually pure by viewing marriage as the finish line, and then anything goes. Just make it down the isle intact, and then your spouse becomes your kinky sex thing, and it's all holy in the sight of God, who looks down on the bed approvingly as your spouse indulges your every fantasy.
Anyway, I'm getting off topic. I have gotten the impression consistently from patristic sources that humanity's sexuality is indeed a corruption and a product of the fall. That is not to say that sexual intercourse within marriage is unacceptable. It is good in that it produces more humans, but intercourse isn't "holy", even under the best of circumstances.
Tapping into that creative potential within ourselves mirror's God's creative nature, and therefore it is an aspect of the divine image within us. However, while I am typing this I realize that all animals reproduce, yet they are not in the divine image, so this ability to procreate might not mirror the divine within us. God does not create a pantheon by begetting himself over and over. Also, if angels can indeed reproduce somehow even though they are bodiless, it can not be a reflection of the image of God, as angels are not created in the image of God. So our creative potential which mirrors the divine image must refer to our rational faculties and our ability to manipulate physical reality around us like no other creature in the created order can.
That being said, even an explanation like the one I just gave wouldn't be proper either, because what is divine within us mirrors God in a microcosmic way. God, according to the Orthodox Church, does not create from preexisting matter, but rather from nothing. We do not create in that way, so perhaps our creative potentials do not necessarily reflect the nature of God.