A couple weeks ago, the American Bar Association's House of Delegates adopted a resolution (PDF) urging states to "eliminate all of their legal barriers to civil marriage between two persons of the same sex who are otherwise eligible to marry."
The American Bar Association is a voluntary association of lawyers whose mission is "To serve equally our members, our profession and the public by defending liberty and delivering justice as the national representative of the legal profession."
Other professional organizations backing same-sex marriage (and/or opposing bans on same-marriage) include the American Psychological Association, the National Association of Social Workers, the American Anthropological Association, and the American Sociological Association.
While these associations do not represent the views of all who belong to those particular professions, having formal institutional support from these groups sends a strong reminder that many experts in law, psychology, social work, anthropology, and sociology are on our side and that we should be seriously questioning the claims of those devout "marriage defenders" who, although loud and opinionated, also hold no expertise in these fields that are extremely relevant to the marriage debate.
One doesn't need an advanced degree in these subjects in order to render a cogent argument, of course. But, the biggest downfall of the "marriage defense" movement is that these folks tend to believe that their "every marriage needs a man and a woman because, um, because uhhhh, god/nature/I say so" argumentation "commonsensically" trumps the more informed and competent arguments of those who actually study law, individuals, society, and families for their jobs in accordance with professional standards.