I've been seeing opposition to Mars in various places (Bill Maher had a surprisingly long rant about it on Real Time earlier this year). I think there are a number of misconceptions some people have about what Elon Musk's plan is for Mars, and people should be ready to correct these misconceptions and be ready to defend the plan, as much as you believe the plan warrants. One misconception I see pop up is that the idea is to flee to Mars because we are destroying Earth. That is an incredibly ridiculous concept, but luckily, that makes it easy to counter. The Pro Mars camp need to be clear that is not a means to escape Earth. Somewhat related to that are the Earth Firsters. On this, as SpaceX is the primary company looking at colonizing Mars, I like to point out that Elon also runs Tesla, a company doing solar, grid storage, gigafactory, EVs, and EV infrastructure, and that's a very big piece of the "stop ruining Earth" pie. So the company doing the most to make it possible to leave Earth is lead by the same guy who leads the company doing the most to improve Earth. In general there's a sense by some that somehow the objectives of saving Earth and going to Mars are opposed, but they are actually aligned in the interest of improving the human condition. At worst, at this moment in time, the effort to make Mars colonizing feasible has helped reduce the cost of access to space, and is saving businesses a lot of money. So to anyone who rejects all other reasons to go to Mars, there's always that.