So what you are saying is that God secretly amended the laws on legitimacy to create a convenient exception for himself. Why is it better to assume additional immorality on God's part rather than just accept that Jesus was technically illegitimate ?
To be honest, the Virgin Birth story probably came from a misunderstanding of Isaiah (largely due to poor translation into Greek) and the Gospel writer's insistence on finding parallels to OT writings.
The Nativity accounts in Luke and Matthew are so different that at least one (in my view both) must be wrong.