Scripture says otherwise.
Psalm 38:3
There is no soundness in my flesh because of Your indignation; there is no health in my bones because of my sin.
Romans 7:5
For while we were in the flesh, the sinful passions, which were brought to light by the Law, were at work in the parts of our body to bear fruit for death.
The flesh is sinful, and those who are in the flesh cannot please God (Rom. 8:8). For the flesh lusts against the Spirit, and the Spirit against the flesh; and these are contrary to one another, so that you do not do the things that you wish (Gal. 5:17). It was not always that way. There was a time, prior to Genesis 3:6-7, when the flesh was good and sinless (Gen. 1:31). Ther was, in fact, nothing sinless in the world.
We're not talking about the spirit. If we were I would tell you that spiritually corrupt creatures do not create spiritually pure progeny.
The Spirit to which that verse is referring is the Spirit of God. Jesus is telling a man born of the flesh he must also be born of God's Spirit...... because he and everything about him is sinful. There is no soundness in his flesh and the sinful passions at work in his flesh work in all the parts of his body to bring death. That would include his penis and his sperm and his wife's vagina and ovum. This is why John wrote those who received Jesus were born, not of blood nor of the will of the flesh nor of the will of man, but of God.