This is fundamentally flawed, and essentially flawed from the Catholic's own arguments on the purpose and nature of marriage and sexuality. That is, all sex acts must intrinsically be ordered towards creation and birth.
If we accept this argument, and understand the mystical nature that is of marriage is one-and-the-same with the sex act of marriage. That is, the uniting of two flesh to become one, and the product of that love as a child.
Catholics and Christians must acknowledge that:
1) The child, the living embodiment of the love and unity of marriage, has an eternal soul.
2) The child has a body that will be resurrected, perfected, and eternal.
3) That child has a unique nature that is specific to the body that his parents gave him - a physical manifestation of their love which is, by the grace of God, an eternal, sub-created nature.
Therefore, at the very least, a fruitful marriage is by God's will eternal in its physical manifestation of the divinely sanctioned union. This is reflected in the Holy Spirit as an eternal person of the Godhead made manifested by the Father and Son's love for each other.
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As a necessary corollary, abortion is, by its very nature, an anti-sacrament or evil act which purposely inverts that of God's will.
