LOL first of all, then why do you think gays are arguing that they have a right to marry?
I imagine the arguments are as diverse as the folks making them. Some gay folks no doubt have valid arguments for gay marriage while others not so much. All gay folks (gays) do not think or act alike.
second what do you do with common law marriage if two ppl of the same sex live together for a number of years. Are they married by common law if one of them says they were in a relationship?
It could be if the state you live in recognizes common law marriages, including common law marriage between two people of the same sex. Otherwise, I would suspect their relationship would not be legally recognized. Surely, someone will test this idea at some point.
THE MYTH: There is a common misperception that if you live together for a certain length of time (seven years is what many people believe), you are common-law married. This is not true anywhere in the United States.
STATES THAT RECOGNIZE COMMON LAW MARRIAGE:
Only a few states recognize common law marriages:
Alabama
Colorado
Georgia (if created before 1/1/97)
Idaho (if created before 1/1/96)
Iowa
Kansas
Montana
New Hampshire (for inheritance purposes only)
Ohio (if created before 10/10/91)
Oklahoma (possibly only if created before 11/1/98. Oklahoma's laws and court decisions may be in conflict about whether common law marriages formed in that state after 11/1/98 will be recognized.)
Pennsylvania (if created before 1/1/05)
Rhode Island
South Carolina
Texas
Utah
Washington, D.C.