Mars is a horrible place to live so I'll take Earth any day. But it would be nice if humanity doesn't get wiped out if we get unlucky with an asteroid.
Frankly, I don't see human society surviving long enough - or perhaps better put, maintaining a necessary level of societal development - for us to develop the tech to establish a self-sufficient colony capable of independent growth and to get us to a planet with the resources to make such a thing possible.
It's hard to make rocket parts when everyone is living in shacks made of sticks and mud and leaves.
You also appear to have an internet connection and a means to use it. Again, technological leaps were required for you to be able to whine on HN.
Perhaps - if you're so utterly sincere and serious about saving the planet as you appear to be - you should be living in the nearest available cave? After all, that minivan is likely to use an internal combustion engine and runs on dead dinosaurs; let alone the plastics and metals and silicon used in said minivan's assembly.
See, this is what I don't get about eco-heros like you appear to be - even if you are homeless, you're still, right now, utilising every single technological leap that it took to get you to the stage of even just living in your minivan and complaining about rocket development on the internet. This, to me, reeks of hypocrisy.
So the most likely outcome of a metaphorical or literal asteroid hit on Earth is that it would still leave thousands, millions, or billions of survivors on Earth, while leaving it unable and/or unwilling to sustain maintenance missions to Mars, so the Mars colonists would starve or otherwise die slowly, despite being technically unaffected by the original disaster.