A Mormon missionary… explained how the practice was permitted by God at various times in history (documented in the OT) and the early Mormon era was simply one more of these times. …
Maybe the larger issue for a Catholic is really that of authority? Any advice would be welcome…
(I did not read this whole thread. I am responding to the original poster).
Yes, the authority is Jesus, Who does not permit polygamy or any sin, ever, for any reason. Also the sin of adultery, practised by Joseph Smith, He never permits, for any reason.
Not-sinning is not just for certain occasions, but for all.
As Paul says in scripture, we are called to strive to be perfect. All the time. Not just sometimes, or convenient times. One cannot be perfect when you are sinning, or putting one’s own lust above the basic needs of others.
Tell your missionary friend that God is the same yesterday, today and always. He never changes.
You also asked for more information on polygamy. The best source is to read the experience of the wives of Joseph Smith. This website:
wivesofjosephsmith.com has the testimonies of his wives (over thirty of them) from approved Mormon sources (the author of the site is a Mormon).
Let your missionary aquaintance read these experiences of these women, and ask herself if she thinks God thinks its okay for women to be hurt and decieved in certain times in history, but not in other times.
And realize also that the self-serving, deceitful, lying Joseph Smith is the author of the Mormon faith.