In light of the Supreme Court's decision that DOMA is unconstitutional, Rand Paul issued a statement including references to humans marrying non-humans.
According to the Division of Public Education on the American Bar Association's website: Hate speech is speech that offends, threatens, or insults groups, based on race, color, religion, national origin, sexual orientation, disability, or other traits.
This is not a freedom of speech issue when it comes to the purposeful insulting of another group, particularly one which has recently garnered specific protections by the Supreme Court.