If one is going to change the definition of marriage to be quote 'same sex ' then there is absolutely no valid argument constitutionally or rhetorically you can make against multiple people getting married. These are radical social changes.
People more than ever since I can remember are concerned about being out of step and out of line with their political party and won't cross over. There is nobody man or woman who wants to be left out and people are fearful of that. People are fearful of their leadership as well.
