system
Given the following post, respond as if you're commenting on Reddit:
human
I believe that nothing is wrong with consensual polygamy. CMV!

What I am not talking about:

A man or woman sneaking around and having multiple families without their spouse knowing about it.

A man or woman cheating on their spouse.

A man or woman being allowed to have another family while their spouse is not allowed to. 

What I am talking about:

An open relationship where if it is agreed upon, either spouse can have multiple spouses.

The only argument I can think of to this is that "marriage is defined as a union between a man and a woman" (aka, the same argument used against gay marriage). Let's assume that this argument is out the window, because it is a religious argument and is completely *invalid* against anyone who does not share that religion, and therefore is not relevant (also I don't believe it's the *most* commonly held opinion in the world anymore).

I am unable to think of any other arguments against polygamy. 

Edit: The general consensus here seems to be that people believe polygamy inevitably leads to supply and demand problems or abuse of the system.

 The supply and demand issue *assumes* that people are not for the most part naturally monogamous, which doesn't explain why the vast majority of people don't go around sleeping with everyone before they're married.

The abuse of the system issue does not address there being anything wrong with polygamy, it only addresses something wrong with abusing the system. This was never really up for debate, it is assuming human nature and saying that we should legislate personal freedoms to prevent people from breaking the law. To put this into perspective this is like saying we should make it illegal to enter banks to prevent bank robbery.
gpt
Polygyny on a large scale has a very bad effect on society, because the richest men get more wives. This makes it impossible for the poorest young men to marry.

These unattached males not only suffer from the health problems single men usually do, but also represent a danger to society because they are far more violent than the average man.

Polygamous men are sometimes not very good parents because they have to spread resources (time, affection, money) on more children.

These families sometimes suffer from constant fighting and competition among wives creating a bad enviroment for children.