I do not support religious reasons for anything. I am, however opposed to government interference on what goes on in anyone's house or bedroom. This has to be an individual's choice and should not be mandated by law. I would not participate polygamy as far as marriage goes but I think that this kind of thing has to be decided by one's own morals and ethics. This should not be dictated by the state or federal government.
Polygamy for religious reasons is valid, and a choice. It shouldn't be illegal if it is not federally recognized. By this I mean a marriage with church and not the state, a holy union (like on sister wives). Polygamy with more then one legal wife would be chaotic for the system, give enormous tax breaks, and be too glamorous for common folk. A man could have two wives in separate states and be married to both, what happens when one wants a divorce?
I, myself, believe I can only love one person as a partner for the rest of my life, but I do not speak for the world. Monogamy is a choice made by someone as is polygamy. Love cannot be labeled as what you or some random guy believes, it's a feeling that comes from within and if someone believes that polygamy is something they inspire to have one day, then so be it. We shouldn't force "moral" beliefs to people as being the right thing yet let people express themselves the way they want to.
Monogamy and polygamy should be self-made choices, not determined by any authority figure. While some will see it as morally unacceptable, that is their opinion and it should not be imposed on others as if it is fact. Polygamy is, in my opinion, irrelevant to morality and should not be punished.