There no reason at all whatsoever to ever say same-sex marriage is wrong. Everyone who says that is obviously not gay and needs to keep their mouth shut. Mrs Clinton is a smart capable advocate for human rights. She is strong and a good role model for everyone and a good voice for the LGBT community.
Hillary Clinton is a very prominent figure in our political world. She is highly respected and people listen to her. A person should be given the right to marry whomever they want to. This is not a religious problem, it is political. An endorsement from Hillary Clinton would be a plus for the gay community.
Same-sex couples should have just as much a right to marry as opposite-sex couples, and by supporting this, Clinton would be standing up for equality. There are many people who would back her endorsement, as well as many same-sex marriage supporters that would have great respect for her, and would therefore vote for her in a possible future election.
While I do not oppose same sex marriage I also disagree that anyone should be forced to say anything they do not want to. Politics are essentially about opinions and public relations, therefore Hilary Clinton should not say anything about any matter unless she does want to.
That's how democracy works.