The animal argument is a bogus one, as animals cannot legally consent and thus can't enter into a contract, which marriage is (beyond the social and religious aspects).
IMHO the genuine argument against gay marriage isn't the kids/dogs/horses argument but the "groups of adults" polygamy argument. In that case legal consent can be obtained because all of the parties are adult and can legally enter into a contract.
LQ
Lizard Queen, this is the best and most rational argument I've heard since I started posting. Thanks for your well thought out argument......its refreshing, even if I don't agree with it completely :)