It is a form of hate, and it is pure bigotry. As is often the case though, the people facilitating it sincerely feel that they have good reason to actively perpetuate this inequality. Most are religious, and it is very telling that they cannot tolerate making their case directly to people, and instead have to rely on making it illegal for others to make a choice they would not make for themselves. You don't see them trying to make constitutional amendments making it illegal to work on a Sunday, or eat shellfish, or take the lord's name in vain, or any number of things the Bible says are wrong. They reserve a special vitriol for gay people, All in defense of an instititution that has, throughout human history, never had anything less than a breathtaking number of variations and definitions, both culturally and legally. It disgusts me.
Every person that voted in favor of that is a moral and intellectual coward at worst, and at best incredibly ignorant. To be fair, the religious indoctrination most of them are acting out puts them squarely in the ignorant camp. Plenty of nice, mostly benign and well intentioned, incredibly ignorant human beings, perpetuating hate.