If marriage is a right given by the constitution, and I am not sure it is, then that right needs to be extended to every consenting adult human being and of course gay marriage would fall under this category and be a right that gay adults should have without question.
This is a country that was allegedly founded on freedom and expression, where is that if we're telling a group of people they're inferior because of who they love? The legal and medical benefits of marriage make it without debate that banning a couple from getting married is putting them at a lower tier, the constitution isn't supposed to support such things.
I am a gay woman and my happiness in life and my value in life is not lesser than that of my siblings who are heterosexual. If my siblings have a constitutional right to get married because it is considered one of the greatest joys in life, then I too must be afforded that right. The person who I love does not affect anyone but ourselves. Another person's religion has no place telling me what is appropriate for me.
The United States constitution guarantees equal rights for all people. Nowhere in the constitution does it say anything against gay marriage. Nowhere in the constitution does it define marriage as a Christian or religious ceremony. By default, gay marriage is a constitutional right in the United States of America, and that's it.
The U.S. Constitution guarantees equal rights for everyone regardless of race or gender. The constitution's vague language states "all men are created equal." Taken literally, the definition of "man" has been redefined several times by Congress. At one time, slaves were counted as 3/5 of a man. Women didn't even have the right to vote. What about homosexual men? Shouldn't they be "created equal" as well? Congress shouldn't have to redefine what a "human being" is ever again. Instead of a constitutional amendment regulating gay marriage, Congress and the states need to amend language of the U.S. Constitution to replace the word "man" or "men" with "human being(s)" in order to clear up any vagueness with regards to rights.
I would argue that no, it is not a Constitutional right, only insofar as marriage in general is not a right that is specified in the Constitution. However, gay marriage should be just as protected as heterosexual marriage, as to not recognize both is to discriminate against a minority's preference, which IS against the Constitution. I also do not think that you can deny a certain group tax benefits because their sexual preferences are different than the majority.