Declare, considers, given - same meaning as a matter of casual discussion, but sure play semantics. I did provide evidence about marriage rights declared/defined/considered/given/protected by the constitution; 14 supreme court cases which declare that marriage as a fundamental right protected by the constitution.
I then just followed the conclusion of your proposal that marriage was not a right because it's not specifically mentioned in the constitution; but I'll expand.
First amendment: "Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof;" vs [relevant part] Fourteenth Amendment: "No State shall make or enforce any law which shall abridge the privileges or immunities of citizens of the United States; nor shall any State deprive any person of life, liberty, or property, without due process of law; nor deny to any person within its jurisdiction the equal protection of the laws."
To argue that marriage is /not/ a declared right of the constitution's fourteenth amendment statement (specifically liberty) is very similar to saying that the specific religion of "Christianity" is not a declared right of the Constitution's First, after all it's not specifically listed. If you argue that the constitution does not protect the specific right of marriage then you have to also argue that the constitution would not protect a specific right to follow Christian teachings/beliefs.
Under such a theory, for example; a Mormon controlled state passes a law that requires all men in the state to marry more than one wife - because the Constitution does not protect the specific freedom of the "Christian" religious beliefs (one wife) on a state level nor does it bar a state from enacting "religious" laws, and because the Constitution does not specifically protect "marriage" as a right - the law would have to be ruled as "constitutional." The only argument one could have against the constitutionality of said law, would be that states are barred from infringing upon personal liberty by the first amendment, but that too would fall into your trap of "marriage isn't a defended right" claim. So, really, as long as the feds (Congress) didn't make the law, the state could do whatever the hell the wanted; including, as I said, decide that Christianity was not socially acceptable and pass a bunch of laws that restricted its practice. Like they could say that only Mormon religions could have tax exempt status, they could argue that Christian marriages performed in other states were not valid in their state, etc., etc.
In order to proclaim that the specific "Christian religion" is protected by the constitution, one has to extend unwritten words into the constitution's first amendment, and similarly we have to extend unwritten words into the protections provided by the fourteenth amendment re liberty. I'm not sure how one can think otherwise frankly.