I think that there is a misunderstanding. Never is probably too strong of a work to use in this situation (in my humble opinion!)

In the Course of Events

Leviticus sets out a number of codes.  There are indeed moral codes, some of which can be found in ch 18 and particularly in ch 19, which have to do with the good of the community, etc.  There are also ritual codes, ie how to properly conduct worship, how to sacrifice animals, etc.  And then there are the holiness codes, intended to set Israel apart from its neighbors.

The neighbors of Israel - Egypt and Canaan, which often fell under Egyptian rule - were considered to be wicked societies.  They were idolatrous, gluttonous, and violent.  If Israel was to be "set apart" - if it was to maintain its holy status as God's chosen people - it had to eliminate all practices common among the neighboring nations.  These practices included human sacrifice, temple prostitution (specifically including male-male prostitution, which is why Lev 18:22 only refers to male-male activity), pederasty, idol worship, etc.  Israel went beyond this to create specialized dietary restrictions and other codes separating its people from the pagans.

Though desert survival may have influenced some of the rules, the primary intention was to set Israel apart from the world.  This was tricky; the Canaanites weren't just neighbors in the sense of sharing a national border.  Rather they were mixed up among the Hebrews on many of the same lands.

The various sets of codes are intermingled in Leviticus.  The diversity of themes even in a single chapter can be dizzying (this may be one of the reasons why many Christians relate to the book as a "flyover" chapter in the Bible, though it actually does have quite a bit of value for us).

We find in Ch 17 rules regarding proper sacrifice of animals, and a stern admonition not to eat the blood of animals.  Those who eat the blood will "be cut off" from the people.

Ch 18 begins with the very reasons for many of the codes of Leviticus: "You shall not do as they do in the land of Egypt... and you shall not do as they do in the land of Canaan....  You shall not follow their statutes.  My ordinances you shall observe and my statutes you shall keep..." 

The chapter goes on to discuss a number of sexual practices, using "uncover their nakedness" as a euphemism for having sex.  Parts of the chapter are strange; Lev 18:19 forbids men from "uncovering the nakedness" of women during menstrual "uncleanness".  The next verse forbids adultery.  The following verse forbids child sacrifice. 

And then 18:22 "You shall not lie with a male as with a woman; it is an abomination."  This line is interesting in that it only forbids anal intercourse between men.  It has no application to lesbians.  Furthermore, the word roughly translated as "abomination" is the Hebrew to'evah, which translates better as "ritual impurity".  Had moral sin been implied, the Hebrew word zimah probably would have been used.

We can also look to the consequences laid out.  The consequence for ANY action listed in Ch 18 is to be "cut off from the people".  This (banishment or shunning) is the same punishment given for eating the blood of an animal. 

This is also the same punishment laid out in 19:8 for anyone who eats the sacrificial meat more than two days after it was sacrificed!  (Anyone accidentally eaten the steak that sat too long in the fridge?  Banishment!)  And we find again in Ch 19 that what is essentially a ritual code (when to eat the sacrificial meat) is preceded and followed by important moral codes (revere your father and mother; save the crops on the edges of your field for the poor).

So yes, Leviticus is a little bit complicated.  However, the distinction between to'evah and zimah, as well as the narrow parameters given in 18:22 and the historical context in Canaan, gives the very clear sense that 18:22 had to do with ritual cleanliness specific to the Hebrew people and NOT with moral uprightness.


Lastly, on your question about polygamy, here is this from religioustolerance.org: Esau had 3 wives, Jacob had 2, Ashur had 2, Elkanah had 2, Solomon had 700 (!), Rehaboam had 3, Abijah had 14.  There are numerous other examples in the Old Testament of men having more than one wife. And don't forget about Abraham conceiving Ishmael with Hagar, Sarah's servant woman.

Women were considered to be the property of men in ancient Hebrew society.  There were many customs at the time, many outlined in the Bible, that we would find to be extraordinarily horrific and immoral.  This is one of the reasons why it is very important to distinguish God's message to us from the context in which it was written.
The Canaanite's Call