After actually getting to personally know (and form a 7 year relationship with) a Witness, contrasted with the supposedly christian people I've met beforehand, I'm dismayed that more people WITH faith don't celebrate it.
She understands that I'm unable to believe, and while she'd like me to attend with her, she knows my reasons for not going to church.
They're honestly happy to have faith, and want to, as they say, "share the good news", but if you don't want to deal with them, just say you're not interested, and you won't be changing your mind. They'll leave, and put a comment about the address for others saying you don't want them to come by. It's really that simple.
It actually opened my eyes to the difference between faith, and religion, letting me see that my problem is with the religion side of things, if faith helps you, awesome. Don't focus on the differences between this church or that church, just be happy when you find someone else with strong faith, I say.
As for greenpeace kids, I'd ask them if they painted their roof silver, to reflect more of the visible spectrum out into space, reducing the portion their roof emits in the infrared bands, which has much less overall effect than the heat exchange between the atmosphere, and the oceans.
Then I'd ask if they ever wondered how the Earth managed to sit in such a delicate balance for billions of years, when all it apparently takes to screw everything up is a hundred ppm of CO2, though the planet didn't enter a runaway greenhouse state when the atmospheric concentration was over 2000 ppm, over 5 times higher than it currently is.
I'm sure that was totally different though, because we weren't alive then to use fear tactics as an excuse to limit the economic mobility of most of the population of the planet in order to maintain a position of power for those who built their empires on oil.