On-topic: I see where the protesters are coming from they believe children raised by same-sex couples would have disadvantages both socially and emotionally. As for the marriage part they find it insulting as they view it from a religious point of view.
I disagree with both, but that doesn't give me the right to insult their opinions. Homosexuality has always been a rather controversial subject throughout history. In ancient Greece for example it was not uncommon for a man to lay with another man and aside from a few laughs nobody really cared, but even "gay men" still got married for society's sake and of course the babies. Now we live in a time where society has become (a tiny bit) more accepting of gay couples and we have several alternatives to traditional childbirth through adoption, IVF and other heretic concepts. The question is just if the acceptance has evolved enough over 2000 years just so gay people can enjoy the concept of family the same way straight people can without being discriminated against financially and socially.