'Our system is messy and complicated, so if we add more variables, it will be an even bigger mess!' - so make the system less messy and enable more variables.
Can you imagine if someone came and said add this function/feature to the program and in response you said "the program is complicated and the code is long, no need to confound it any further with features."
I don't see what would change such that it would introduce any new complexity on that side of things.
The exact same complexity already exists today: step-parents. It's mostly a non-issue and is well defined. Step parents acquire no custody rights over the child inherently. If my wife remarries, and we had a child together, the parental rights are retained in myself and her. The same would be the case in a three-way break away on that ten person marriage; there would be (in this scenario) a two person custody of the child, eg the biological parents.
Again, I'm not saying this argument is valid or should carry the day, only that it is defensible and non-bigoted.
Nothing changes about the legal custody system of children due to N-way marriages.
If two people in the N-way marriage have a child, it's not the N-way marriage that acquires custody, it's the two biological parents.
Marriages do not define custody, period. That is not how it works in the US.
Keep in mind that presumptively is not definitively. If there is a paternity test that later says otherwise, eg if your wife or husband cheated on you, then that other person can typically acquire parental custody, because they are the biological parent. All things being equal (not involving abuse or danger to the child), biology is the first line of legal custody.
What about adoption? The most sane thing to do near-term, would be to keep it the same - adoptions are max two people legal scenarios. If the system is cleaned up, simplified, or otherwise adjusted for N-way marriages, then perhaps later there could be N-way adoptions as well (and scientifically, we may eventually see N-way biological custody too).
Vague metaphors aside, this happens occasionally in the industry I'm in (finance) when we trade small lots of non-traditional products. These products don't follow many of the rules that all of our other traded products do. Instead of re-writing our systems to deal with these(totally impractical), we manually shimmy these in to the database until they expire or are traded away, at which point we can forget about them.
And yes, I read Moon is a Harsh Mistress too many times (I'm a sucker for that novel). :P
I think it would be wise to consider the possibility that maybe the legal institutions involved in marriage aren't up to scratch in terms of what humans can possibly do in terms of romantic and intimate relationships. It's better, in my opinion, to incorporate a method by which we can address these issues by more effective methods (as in don't ban something just because you don't like it. You ban it because it's destructive to the social order.).
The social and psychological aspects are still scarce since we live in a society built around western European Protestantism (heteronormative). So, whatever research that does exist is relatively new or limited in scope.
Of course. On my list of social causes worth spending time and energy on, polygamy ranks pretty low. If it's near and dear to your heart I wish you the best of luck.
If the white male religious nut case can provide and care for the woman and any resulting offspring and the woman are willing and knowing participants in the harem.
What's the problem? That you don't like it? That seems rather bigoted.
I could be wrong. I haven't done extensive research into this. If you want to convince me, show me the data.
If anything, it should be you that should go and create a research program analyzing the nature of poly relationships in humans and the underlying causes, not me. I merely pointed out the reality that our law should consider accommodation for those individuals as it does for others. All you seem to be bringing to the table is scare mongering that depends more on the tiniest of slivers of human society for the proposition that poly relationships should be illegal. Such a proposition is not tenable on it's face nor in its contents thus far. Or in simpler terms: please do your own research because I'm not here to convince you either way (but you seem damn sure to convince me that my poly friends are some evil bad fundies wanting to rape children).
Edit: sorry for the rudeness. I take things personally sometimes.
There are two large groups: one with a pretty 'dirty' record regarding abuse/child marriages and another with a clean record. So this could come down more to an environment/community issue than a polygamy issue where, in one community/environment, abuse and child marriages are largely the norm and the other it isn't.
Warren Jeffs' Fundamentalist Church of Jesus Christ of Latter-Day Saints && Apostolic United Brethren. The former having the bad record and the latter having the clean record. (&& being the separator to avoid confusion) The former is larger than the latter but the latter is the second-largest church that practices polygamy.
E:
The burden of proof is also on you to prove that polygamy leads to abuse/child abuse as you are the one making the claim. Given there's little/no data to support either side, you'll have to wait for more research. Which would likely involve legalizing the practice and conducting studies.
The easiest way to resolve the child situation would be to keep custody to two parents as it is today. Any children that exist in the N=5 marriage, would be biologically between two people. So the only thing that would be changing is marriage itself, not child custody laws (which today are not primarily built on marriage anyway, we can obviously marry other people that have pre-existing children without adopting those children as our own; and we can obviously have children outside of marriage).