Polygyny, Infidelity, and Multiple Girlfriends: What's The Difference?

During a recent interfaith panel discussion on marriage, a question was raised about Islam's approval of polygyny: "How can you people say you're moral when your holy book tells men they can cheat on their wives and have up to four women. Don't you all believe in polygyny?" Then, another man joked, "I got four girlfriends. I could be a Muslim!"  There is a distinct difference between polygyny, infidelity and multiple girlfriends, but in a society that permits the last two but bans the first one, most men and women don't know the difference. So today we want to explore the honest intentions and cooperation between women in a polygynous family and how that differs from the deception of infidelity and the dishonesty and competition between women when a man merely has multiple girlfriends. The reason for polygyny as given in the Holy Quran is to compensate for the massive loss of men during war, leaving many widows and orphans. Violence, disease and incarceration has led to massive loss of men in this time, creating the need for polygyny to give women husband and children fathers. What qualities in men and women are necessary in order for the society to change from dishonesty and competition to honesty and cooperation? Are our religious beliefs helping or hindering that process?