Their baptisms are useless. The first Baptism is what is important.
Of course their (Mormon) baptism is useless. Just like your Catholic baptism.
Look. The Bible is quite clear and specific on baptism.
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Ephesians 4:5-6
King James Version (KJV)
5 One Lord, one faith, one baptism,
6 One God and Father of all, who is above all, and through all, and in you all.