Anybody that wants more than one spouse has to be out of their mind but as far as morals go it is a very grey area. If they can make it work then I say go for it but it does create a lot of confusion and it a hard pill for society to swallow.
We base a lot of our morals on our culture. If you choose not to have a polygamous relationship that is fine. For those that do, it doesn't affect you in any way and there are no victims - everyone made a choice (If someone is forced into that situation, then it may be morally wrong to me). Culture changes over time, but only in small increments. The morals of a a male from one culture is not the same as my morals. For example, in some cultures beating your wife is morally acceptable, whereas in my culture it is not. My morals I set for myself is that every human should be equal and as long as there are no victims then there is no point in having morals condemning a choice.
Polygamy is a choice that some people make, and it works for them. There is nothing that should prohibit this practice so long as it is occurring between consenting adults. Many polygamous families live happily and in harmony with multiple spouses, and truly enjoy the benefits reaped from such an arrangement.
Countries should stop trying to legislate morality and behavior that does not harm others. Polygamy should be a rightful choice that legal, consenting adults can chose to practice if they wish. Polygamy is not a moral issue, but a personal choice between adults. Some might believe that a traditional marriage between two people is stifling. Therefore, adults should have the right to practice polygamy if they want.
As long as every party is consenting, it is not morally wrong to enter into polygamy. There are many people who enjoy a polyamorous relationship. It should not be against the law for these people to marry. They should enjoy the same rights as anyone in a monogamous two-person relationship.