By whose authority? Why would they be excommunicated for living the law of celestial marriage as outlined in D&C section 132:4 For behold, I reveal unto you a new and an everlasting acovenant; and if ye abide not that covenant, then are ye be damned•; for no one can reject• this covenant and be permitted to enter into my glory.
"the doctrine of plural and celestial marriage is the most holy and important doctrine ever revealed to man on earth, and that without obedience to that principle no man can ever attain to the fullness of exaltation in the celestial glory" (William Clayton in Historical Record, p.266); "the only men who become gods, even the Son of God, are those who enter into polygamy" (Brigham Young, in Journal of Discourses, vol. 11, p.269)
"To enter the celestial [kingdom] and obtain exaltation, it is necessary that the whole law be kept...Do you desire to enter the celestial Kingdom and receive eternal life? Then be willing to keep all of the commandments" (Joseph Fielding Smith, in The Way to Perfection, p.206).
On October 12, 1856, Heber C. Kimball (first counselor to Brigham Young) declared, "You might as well deny 'Mormonism,' and turn away from it, as to oppose the plurality of wives." (JOD 5:203).
1880, Mormon Apostle Orson Pratt said, "...if plurality of marriage is not true or in other words, if a man has no divine right to marry two wives or more in this world, then marriage for eternity is not true, and your faith is all vain, and all the sealing ordinances, and powers, pertaining to marriages for eternity are vain, worthless, good for nothing; for as sure as one is true the other also must be true." (JOD 21:296).
BTW I don't believe any of the claims by the LDS or the LDS offshoots, so I won't be joining anyone in Texas! It's just funny to me....the pot calling the kettle black!
You cite ancient history. Polygamy was abolished before UT became a state and is against state and federal law.