Ok then. Logically.
1) All American's are granted equal rights under the 14th Amendment
2) At the federal and state level there are thousands of different tax, health etc. benefits related to marriage status
3) There are a minority group of American citizens who are sexually attracted to, and thus sometimes wish to marry, a person of the same sex. Even IF (and this is hypothetical mind you, there's overwhelming evidence that sexual orientation is influenced by genetics) this is a choice, it is a choice made among consenting adults who are not harming the rights of any other citizen.
4) So by logical progression, do not these people deserve the same benefits as heterosexual couples?