The fears of the slippery slope have no basis. The commitment remains the same, with a person choosing to enter a commitment with the person (s)he wants to spend the rest of their lives together.
Polygamy is not in the issue because it involves more than two consenting adults and completely changes the nature of the commitment and the relationship. Marrying an animal is completely different as animals are not able to express legal consent to any action.
People are spreading fear and paranoia as propaganda tools against gay marriage. They make no logical sense.
