Just remember that the "Yes on 8" people are advancing the meme that it protects marriage. Just remember that by voting "Yes" on 8 you are actually removing the option of marriage from many of your fellow Californians.
So if you really want to "protect marriage" you have to say "no" on 8. Compare it to a situation where you want to get a pie that you could share with anyone that wanted a slice. In this case by saying "yes I want pie" would meant that only some of the people would get a slice of the pie. In this instance you have to say "No" in order for every one to get a slice of tasty, tasty pie.