Does the Christian idea of marriage in America discriminate against Muslim marriage?

People are always railing against the traditional marriage idea in America because gays can't participate but what about muslims? The Muslim concept of marriage has always accepted up to four wives, the marriage of girls at VERY young ages (because mohammed's second wife aisha was 6 at marriage and 9 at consummation) and very commonly are to family members (first cousins and even sisters). My question is on what basis do we tell Muslims (or any number of other culture's) that their idea of marriage is wrong? Our country has always gone by the Christian ideal where two people of opposite gender, similar age and different families marry. This has eliminated polygamy, child marriage and , all elements of Muslim marriage. Atheist friends of mine have no logical reasons to protest and actually support these other forms. I as a Christian have principles to stand on. Any other form of "marriage" isn't what society should aim for and they all have serious negative consequences.