You are making an assumption that marriage should be any two people. Who are you to judge those who wish to live in polygamy, for example? You are not adhering to your own standards. You would define marriage as any two people. Your definition also discriminates against some people. Why would you limit marriage to just two?
On the one hand, you say that nobody has a right to tell anyone who they can or can’t marry, but on the other hand, you apparently want to see marriage defined in a certain way. Those who wish to preserve traditional marriage also want to see marriage defined in a certain way. You have a lot in common with the marriage traditionalists.