Abolitionists succeed in abolishing slavery in about 50 years. Dream achieved during lifetime and seen impossible at start.
You have to recall that the abolition of slavery was largely a political goal argued for in the USA and UK using Christian terminology, but in French colonies using secular terminology, and is considered so important largely because it is a political founding myth of the post-civil-war USA.
It was permitted to succeed because it served the purposes of the growing secular State, and the humanitarian achievement is (in the eyes of the State) just a side effect. It was achieved in different places at different times by both Christian activists and humanitarian secularists.
Certainly it had many positive effects. Yet at the same time it reduced the power of "tribes" (individual powerful families), and created a permanent social underclass who became ultimately dependent upon the State rather than the wealthy and able to be used by the State for various ends - as you've seen over the past few years with this class being incited to rise up by BLM. The West is now ruled by totalitarian governments that could never have arisen without the welfare state that abolition cleared the way for.
Satan had plans for it, so he supported it, and it happened.
I would argue the correct Biblical position would have been to restrict it to a point of near-abolition as per the scriptural laws - freeing all who were enslaved by force (e.g. the blacks in the USA), but leaving a limited version of the institution available as a solution for the poor who could choose to sell their services for a fixed period of up to 7 years for an advance payment, with strict labour laws around corporal punishment and hours etc. That would have eliminated the evil while restricting the rise of the State, by keeping in place a decentralised social welfare system that avoided the creation of a politically useful social underclass. But that's not what happened. Instead a more radical and simplistic goal was adopted, the baby was thrown out with the bathwater, and good Christians seeking only to help people unwittingly laid the foundations for Marxism.
Does Satan have plans for social acceptance of polygamy? If so, it might happen too. If it happens for that reason there will be short-term benefits but the end result may not be what we hope for.
The Biblical goal would be for the promotion of only those relationships that are not sinful, but retaining those restrictions against things that are truly sin - partial sexual freedom, partial abolition of marriage restrictions. Satan's goal is more radical - complete eradication of the very concept of sexual crimes from the entire legal system. That he will use as a tool to destroy society. Full legalisation of polygamy will no doubt occur if that goal is achieved - but don't get excited about it, as the social harm of the whole package will be greater than the gain, and persecution of conservative Christians will continue, the excuses will just change. We may be persecuted for patriarchy instead of polygamy, for instance.