Worship the Truck Farmer At the Church of Your Choice!!
I am all for conserving the planet because while I am a huge believer in the "Earth has always and will always be here" mentality, I don't believe that it includes humans. Earth was fine before humans and it will be fine after humans.
The main reason I don't want humans to go to other planets and attempt to colonize them is strictly because of Earth conservation. If we have Mars or the Moon or another place as a "backup Earth" then why save this planet? People who have the ability to will be able to leave while the others remain. I don't want our planet to wind up in some kind of Wall-E scenario because that movie was too long and drawn out and would've worked better as an animated short and I don't want that for our home.