Basically, Supreme Court has been filled up with people that share the president's agenda, an act that is not exclusive to President Obama. Supreme Court's job is to translate the US Constitution, and to make decisions on certain things based off the Amendments in said Constitution. Gay marriage is never mentioned in the Constitution. In fact, the right to marriage is not included or addressed in the Constitution at all. Supreme Court cannot legally address topics that do not fall into what the US Constitution entails. Instead, they weaseled their way out of it by using the 14th Amendment to say that it is legal. The sections of the 14th Amendment that are related to this topic are as follows:
Section 1.
All persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States and of the state wherein they reside. 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.
Section 5.
The Congress shall have power to enforce, by appropriate legislation, the provisions of this article.
Notice how vague Section 1 is. The Constitution is infamous for this. Amendments are vague, which is why we have 27. Also take into consideration when this Amendment was added. Right after the American Civil War. You know, enslavement is bad. The 14th Amendment regards slavery, but because it is so vague, we have the 15th Amendment, which specified that black men could vote. Doesn't that information technically fall into the 14th Amendment? The answer is, we don't know because it's so freaking vague, so we need to make more amendments. That's why we have the 19th Amendment, which specifies that women could vote. Wasn't that already covered in the 14th Amendment? Answer: It's too vague for Supreme Court to do anything.
But now we have Supreme Court using the 14th Amendment to legalize gay marriage; they only specify gay marriage, mind you, as if normal marriage was already in the Constitution, which it isn't. Marriage and gay marriage are not mentioned in the Constitution, and Supreme Court does not have the authority to make decisions regarding them. Instead, the Legislative Branch should have written in a new 28th Amendment, specifying that marriage, between any two human individuals, is protected under that US Constitution.
EDIT: And if we go by Supreme Court's decision to use the 14th AMendment, that means only people born in the US are allowed to marry. If you come here from another country and become a citizen, tough luck.
Edited 1/1/2016 21:20:02