Well evidently you must know something about them that I don't, so I guess you must know them personally?
I don't need to know them personally to know there's a difference between:
Group A: People who believe in a lifestyle due to a religious/personal calling, who engage in a plural relationship where all participants take part in the selection and inclusion of a new spouse and conduct themselves in a manner that is consistent with their personal beliefs and religious calling and operate by rules within their marriage and their faith to make sure that it's as successful as possible given the circumstances.
and
Group B: A husband who steps out and has an affair and a wife, who doesn't want to put her foot down and force a choice (less the choice be not what she wanted) who emulates the practice, but not the beliefs, teachings, or faith, of a group of people she sees on TV by taking into her household the mistress and calling her a "sister wife."
Contrary to what is running with group A, group B is simply entering into an arrangement that works at the time for all parties. The moment the husband gets bored with either woman, the other woman moves on, or the wife is sick of the arrangement, it will end. Nobody is feeling a calling... The wife just doesn't want to divorce, the husband has no reason to disagree because happily gets both of his options, and the other woman can stay around or go as she chooses. Despite their different marital dynamics, for couple A, the selection of another wife is a group process and not simply a man going out and marking a woman as his and bringing her home, spending all of his time (or a majority of it) with the new wife, then moving on. They have schedules, responsibilities, obligations, etc etc. If the seed of a marriage or new wife had started for group A as it did for group B, the wives would have deemed it an affair and rejected her.
Group A is committed to each other, the belief, and it's practice. Group B is not. Therefore, when things get hard, which they will, group B has no reason to invest in it's solution. Group A does. So, as I said, group B's issues will work themselves out.
I don't know why you're being snotty about it to me, it's just common sense.