To make it your life mission to improve the lives of gay people, talking to people IN California about Prop 8, extending that advocacy across the country, and then some asshole sees that you posted a billboard and says “pfffft, that’s nothing”. That’s miserable.
Entrenching yourself in a culture that finds your views abhorrent and changing minds is one of the best things you can do for advocacy. You can’t do much in a bubble full of people who agree with you.
EDIT: Here’s Missiongathering’s site. They seem like good people.