Pure speculation on my part: If the bolded were the case,wouldn't it have happened already?
More speculation: Considering what I've seen and experienced of today's younger generation I expect polygamy to be legal within 50 years, perhaps less. The "youngsters nowadays" are, from what I've noticed, much more open about their sexuality and much more willing to cross traditional gender lines. I don't think it's my place to say whether it's a good or a bad thing.
Please keep in mind I'm not saying this is a universal truth, just impressions I've gleaned from my limited experience: I'm just musing out loud here . . .
Maybe it will be a straight line, onwards and upwards into Big Gay Al's Fabulous Future. OTOH, maybe not.
ProsperityAnti-normative behaviors are like obesity, heart disease, gout, and other diseases of affluence. They multiply in times of affluence and atrophy when times get tough. Folk don't have time for such when they don't know where their next meal is coming from or if they have to worry about random violence. And they are less likely to test the patience and tolerance of friends, family, and neighbors is such situations. Solitary people without a blood-tie community are less likely to survive. If our economic system takes a serious hit, such trends will slow or reverse. For example:
1. Peak of Roman Empire vs the tribulations of Rome's decay and the follow-on Germanic kingdoms.
2. 1920s vs 1930s America.
Fourth Great AwakeningPeriods of hedonism and dissipation many times are followed by periods of re-dedication to an objective and eternal moral code. We have had three thus far in America. We may have another before America crumbles and is swept into the dust bin of history.
IslamAlthough some muslims in some places practice homosexuality and pederasty with abandon, most of the more orthodox sort take a dim view of it. Pim Fortyun, the Dutch politician and homosexual pederast who called for closing the border to any more muslim immigrants because he feared more muslims would endanger his sexual activities (among other reasons). Given that when orthodox muslims took power they would put homosexuals and pederasts on trial and then kill them, he has a point. We see more & more muslim influence on european society and social policy. It remains to be seen if it will win out. the two alternatives are:
1. Islam triumphs
Or, alternately, the West commits suicide and Islam moves into the vacuum. Expect homosexuality in all its manifestations to be re-criminalized and those places where it has infiltrated social mores to be rooted out.
2. Ethno-Nationalist Resurgence.
We do see ethno-nationalism gaining strength to fight against the progressive project (which includes mass immigration and western decline). From UKIP in the UK to Golden Dawn in Greece, it is currently waxing in influence. If it triumphs or influences the other parties, this might attenuate muslim infiltration and influence. Not all of these have a socially conservative element, but some do, so continuation of the trend to more & more dissipation is indeterminate.
Polygamy
I'm bigger, stronger and more well armed than you. Make me a Sammich!
Well, they presumably also had slaves. Or were slaves.
Pretty much.
Polygamy is a stable arrangement only when men are almost completely dominant and women chattel or near-chattel. None of that-thar silly suffrage or equality (under the law or anywhere). Otherwise, too many egos and agendas and personalities like strings mentioned.
Were it to become more common and more normalized, the taxpayer would soon become a party to the relationship as the taxpayer would pay the clean-up bills and most the other costs. We see some of this in the underclass with males knocking up several women in series or parallel and each woman and child getting on welfare. We also see the welfare-usage in the polygamous Mormon offshoots.