Being conceived in lust is the sin. Christ was not conceived in Lust but was brought forth by the Holy Spirit overshadowing the flesh.
Excellent point us2are1.
The problem is that we are failing to grasp what it means to bear the flesh which belongs to Adam. In the discussion of Melchizedek I came across a scripture which actually conveys the thought of how we also bear the sin of Adam to our flesh.
It speaks of the seed that is Levi as being in Abrams flesh when Abram gave tithes and thus says Levi also gave tithes.
Get your mind around that and I will go find the verse. here it is:
Hebrews 7:9-10 "And as I may so say, Levi also, who receiveth tithes, payed tithes in Abraham. For he was yet in the loins of his father, when Melchisedec met him."
That is the sense of how we bear Adam's sin and why we also bear Adam's punishment for sin though not having directly committed that sin ourselves.