Perhaps this question is best left until a generation or two before we have reliable evidence to conclude either way what is acceptable in terms of risk-analysis and of social acceptance. 100 years ago, it was perfectly acceptable for a man to have a mistress on his side, but was socially exiled for getting a divorce and then remarrying (and then having CHILDREN in his new marriage
). Nowadays, we don't give it much thought outside of some musings about couples staying together for 50+ years and how much better that was.
But polyamory as a phenomenon is still very recent.
How I see it at least. Give it time before it can reliably be put forward as part of a meta-analysis to compare and contrast it to monogamy. I'm still a "live and let live" kind of gal, though.