Why can't they marry?

I’ve never seen the justice in the case against gay marriage. It seems un-American to withhold a right of free expression that does no harm to other groups, and gay marriage is not a threat to any group in America, and certainly is not a threat to the institution of marriage. Marriage once represented a bond between a man and a woman as a way to tie together the two individuals as they use their relationship to continue the species. However, in our current times so graced by technological innovation, families can be created by adoption and artificial insemination. Marriage has changed from an institution for the preservation of the species to one that can be based solely on an expression of love for another. Also, the Declaration of Independence stated the inalienable rights as life, liberty, and the pursuit of happiness. In this way, gay marriage is a way of living the American dream because it is a way for two individuals to create happiness and success by their own actions. Plus, any law by Congress or by a state against gay marriage would have to be unconstitutional due to the right to privacy that recent Supreme Court rulings have seemed to add to the 14^th Amendment because the government has no place to dictate the private lives of citizens who are doing no harm to others. In the end, marriage is a right that has been withheld from the gay community for reasons that I can not make sense of. Religious complaints hardly seem like a valid argument for alienating a group of people and it is politically incorrect for our government to place religious views in front of all of the different ideas of their citizens. Equality is what the nation was founded on and equality is what its population deserves.