You just answered your own question.There has to be a stopping point to most everything. So when is the stopping point to equality? Beasteanity? People that love their animals could make just as good of argument for love an equality as gay PEOPLE can about marriage.
You see, an animal does not have the ability to consent to a marriage contract. Never has. Never will. Only adult humans in their right minds have that ability.
Now, can you answer me why so many anti-marriage folks like yourself have difficulty in understanding the legal and cognitive differences between humans and animals? The rest of us just don't get that.