And just what is wrong with a union of two male gerbils, a female great Dane, a boy, and a woman? How about three men and a feather duster? If the touchstone of "legally recognized union" is whatever floats your boat in private, then the results are clearly ridiculous.
You're confusing libertineism with liberty.
Liberty doesn't mean anarchy. Society has a right to set moral boundaries, and it's exactly the reason we have laws against rape, theft and murder.
Homosexuality promotes an unsanitary, unsafe, promiscuous lifestyle that is dangerous to the health of the overrall population, let alone the dangers to themselves because of the activities they engage in.
Society has every right to define moral boundaries and to prevent deviant, degenerate members of society from inflicting their moral sickness on the rest of the country.