Thoughts after Karen's post:

I think the people really against it are just against homosexuality completely, and they feel by keeping the marriages illegal they are at least putting a curb on something they feel is wrong. Some probably tell themselves they are defending the institution of marriage and believe that but in the end I think it just comes down to a lifestyle they don't agree with and they think legal marriage will make it more accepted.

I think the "it wrecks the institution of marriage" argument is easier for them to say than "I don't like homosexuality and don't approve of anything that supports it and makes it acceptable in society."