I voted you up because i believe this is a valid question, even if I don't agree with the conclusion you have come to .

–Anon_69E0A63BD has, to some degree, have you read it through? This part is particularly telling: (Matt. 19: 4 - 6)

He answered, “Have you not read that he who created them from the beginning made them male and female, 5 and said, ‘Therefore a man shall leave his father and his mother and hold fast to his wife, and the two shall become one flesh’? 6 So they are no longer two but one flesh. What therefore God has joined together, let not man separate.”

Part of the problem withAnon_69....'s answer is that some context is left out: Matt.19:3 The Pharisees also came to Him, testing Him, and saying to Him, “Is it lawful for a man to divorce his wife for just any reason?” This passage relates to divorce directly, but to the issue of polygamy only indirectly. In the First Century, the Pharisees and Sadducees had already come to the conclusion Roman rule and the difficulties of providing for all wives justly (one couldn't diminish a first wife's rights to clothing, food or marital rights, otherwise she could go back to her parents (or brother, if they were gone) and take her 'bride - price' with her.) made polygamy too difficult. The conditions are equally difficult today.

My primary Scriptural argument, which was not mentioned by –Anon_69E0A63BD, is the argument from the two greatest commands: Matthew 22:36 - 39
"Teacher, which is the great commandment in the law?”

Jesus said to him, “‘You shall love the LORD your God with all your heart, with all your soul, and with all your mind.’ “This is the first and great commandment."

“And the second is like it: ‘You shall love your neighbor as yourself."

“On these two commandments hang all the Law and the Prophets.”

Along with Paul's statement : Eph.5: 25 - 31, Where Paul describes the standard for Christian Marriage:

Husbands, love your wives, even as Christ also loved the church, and gave himself for it; That he might sanctify and cleanse it with the washing of water by the word, That he might present it to himself a glorious church, not having spot, or wrinkle, or any such thing; but that it should be holy and without blemish.

So ought men to love their wives as their own bodies. He that loveth his wife loveth himself. For no man ever yet hated his own flesh; but nourisheth and cherisheth it, even as the Lord the church: For we are members of his body, of his flesh, and of his bones. For this cause shall a man leave his father and mother, and shall be joined unto his wife, and they two (not more, see Genesis 2:24) shall be one flesh.

This is a great mystery: but I speak concerning Christ and the church. Nevertheless let every one of you in particular so love his wife even as himself; and the wife see that she reverence her husband.

It is a call back to the Creation mandate, where we didn't have the full consequences of declining fertility, and one man was married to one wife. Paul amplifies Jesus' meaning when he said that a husband was to love his wife as himself. (You would not want an 'open marriage' with out your consent, would you?) Seriously, I won't downvote this, partially because I think simply saying polygamy is not for today is too simplistic, and partly because i think there are some reasonable times when polygamy should not be excluded as an option:

1. Married man in country where polygamy is permitted (and even encouraged!) finds Jesus, and his wives (all of them) are content to remain with him. According to 1 Cor. 7, It is recommended they remain as a whole family.

There are likely others, but this is the strongest one I could come up with, currently.