It is a very legitimate question.
There are many Christian sources who try to cope with the fact that many important patriarchs in Old Testament were polygams and that polygamy is not explicitely forbidden in the New Testament, as anyone can see there for themselves.
I suppose that they try to make the Bible tell what they would like it to say.
For instance:
http://www.eadshome.com/polygamy.htm
Some Moslem scholars seem to present good arguments for the absence of an explicit prohibition of polygamy in the Bible. (Of course, their intention is to support the idea that the Christians have no reason to criticize polygamy in Islam)
This is developed in the following source:
http://www.quransearch.com/ntpoly.htm
The Mormons fundamentalists (not the Latter-day Saints) support polygamy too, but their main reference is not the Bible but the Book of Mormon.

Of course, my answer could shock:
- "people who try to make the Bible tell what they would like it to say" (for instance, supporters of the view in my first reference)
- people who do not understand why Moslem scholar should have something to say about this issue
- Mormons (LDS) who could feel hurt if I am saying that the main base of their religion is not the Bible, but first the Book of Mormon.
- Bible fans or people lacking lateral thinking who would consider that I should have looked for answers exclusively in the Bible, building my answer out of a serie of Bible quotations.

It is not my purpose to shock these people. There have already many occasions to be shocked every time that they are leaving their own universe.
I wanted maily to address those who have broader views, and present them interesting elements about the issue, which you could not obtain if you were limiting your field of research.

(Answer to Ethernium) Come on, brother! Learn to properly divide the Bible... In 1 Kings 15:5 it is said that David had not turned aside from anything that God had commanded except in the CASE of Uriah the Hittite. The CASE included the precursor of lust, coveting his neighbors wife, and adultery. You are not defending those, are you, just because they are not mentioned specifically? The case also included plotting, deceit, and selfishness in the murder of Uriah, for which I'm glad this CASE took it's namesake as otherwise poor Uriah is almost forgotten... And the case ends with a polygamous act of David's marriage to Uriah's widow. I think we can reasonably assume that this Bible Patriarch indulged in several forbidden practices here. Case closed.

The bible doesn't specifically forbid it however if you look pretty much all the instances where men had multiple wives. (There actually arn't that many) it turned out pretty bad. Look at Leah and Racheal

Hi WoundsofAFriend !
You have made some very good points.
I do have one thing to comment on. The word "gay" is a man-made-term. What Jesus called those who have the personality which renders one( a-sexuality)which is what I describe one as, is "EUNACH". This term is not of the normal language of today, but I feel adequately describes a "gay" person.

Most people who are gay are just not into the opposite sex seeking-mode-of-behavior. This usually evolves into what is now called "gay". It is because of mankinds lack of knowledge on the subject which erroneously placed eunachs into a class of seeking love, acceptance,affirmation, and physical-erotic-satisfaction from the same sex. Most societies label those who have been given a gift from God of being a eunach, as: "gay,funny,homo,dyke,he/s he,fruit,......" from the beginning of civilization.
Evil,self-seeking-pleaure hunting- perverts, have preyed on those who were made different from some males/females. Evil has deemed these precious,gifted persons as (GAY!).. Perversion and sexual deviation has been imposed upon these persons , as an answer to what they have been told is abnormal or a paramount problem in their lives, because they do not fit in to the role(s) society has fashioned they should play in their society.
The word
Gay means " grieving Adonai Yahway" or Going against Yahwah(God). Satan has always used words to confuse God's people.
I choose to call the celibate gays who choose to go against the grain set by satan by doing what the bible says, GAY means God's annointed Youth. This is what they were before the world perverted their way of thinking. Remember spirits can try to control people who are different by making them believe a lie and bringing people into that person's life who will make the negative things they prophesy happen.
BiBiRaRi