You ought to. His words are part of the Scripture and his prophecy was the prophecy of God.
However, his words are far from an endorsement of polygamy.
Basically, Nathan says that God is saying: "Look David, I gave you all kinds of things - authority, kingship, victories, lands, wives, anything you could have wanted. But you killed loyal Uriah and took his wife for yourself. You've gone too far and I'm punishing you. I'm going to kill your son."
This is hardly a pro-polygamy peptalk. It does no reference plygamy in any positive way.
>>So Abraham was committing adultery whenever he slept with his concubines.
No, a Concubine had the status of a wife, just not the right to inherit.
(http://dictionary.reference.com/browse/Concubine)
The meaning of the word concubine has changed over the centuries, back then it had this meaning:
2. In certain societies, such as imperial China, a woman contracted to a man as a secondary wife, often having few legal rights and low social status.
See the word wife in there? I do.
>> A concubine is not a wife. That would be adultery.
See above, you are incorrectly applying the word from today’s use to scriptures written in another era. When the word meant something else. Abraham was not an adulterer.
>> Hagar was no blessing to Abraham.
I disagree.
>> The Arabs are the punishment for that sin.
Got Scripture?
No?
Got Speculation = Got Nothing.
>> And frankly I don't put much stock into what Nathan said.
2 Sam 12: 1 AND the LORD sent Nathan unto David….
Um he was a prophet… Why do you read the Bible? Do you realize that it was written by these guys who were prophets?
>> Anyone can say anything and claim it came from God.
Um, yes, there are even people who think they are God, those whose writings are accepted cannon of Christian churches more than 2000 years later, however are a much smaller group.
As for me, I’m gonna go with the bible on this one, wait! That’s what this whole discussion is about! You are saying the bible does not support Polygamy, by ignoring parts of the bible and saying “And frankly I don't put much stock into what” you might as well end with “the bible says” here.
>> Anyone can say anything and claim it came from God.
Get thee behind me Satan! There is just so many ways I could play with this statement, but most involve me claiming to have revelation from God and my pursuit of humor breaks off where I would have to gross the line of Blasphemy.