Thus the Immaculate Conception. Her stainless soul was absolutely required.
If you say then that God could have made it possible, then why can you not say that God made it possible for Jesus?
If we're going to discuss "possibilities" we could also state that God could have fashioned His own flesh out of dust like He did with Adam. He didn't need to be "born" into a nuclear family, but He chose to. He chose to have a mother and a foster father and to grow and learn like all of us. Why's that? If Mary isn't worth venerating, she certainly wasn't worth being born through, right?
The logic isn't off at all; it simply follows the trail of facts.
No, it needn't be that Mary's parents were created sinless, and that is not what doctrine teaches. But it is perfectly logical that a mother, who donates DNA to the child she bears, need be sinless if the child is to be truly sinless.
Jesus wasn't conceived apart from his mother Mary. She gave Him His flesh. His sinless flesh. There was only one way for that to happen: she needed to have sinless flesh to give.
Yes, perhaps Jesus could have been "created" sinless by some suspension of nature, but then, He wouldn't be fully man, would He?
No, Mary's sinlessness isn't a suspension of nature: it was a restoration of man's original condition; or a preservation of it in her case.
I realize I'm leaving open the question of why Mary's parent's needn't necessarily be sinless; for me, I'm satisfied with the doctrine. However, perhaps on reflection either myself or someone with some real sense can address it for you. I apologize; I'm a bit too busy at the moment and some things are best not forced.