Well, there's the simple fact (or what seems to be a fact at least, might not be true) that the reality of physics confines us to this rock, more or less. We don't travel faster than light, so at best we can achieve a Mars colony dependent on Earth supplies.
So yeah, I'd rather just focus on developing survival strategies for our rock. But the whole discussion is maybe a bit off topic here too.
A self-sufficient Mars colony isn't easy, but it doesn't seem impossible. And the lack of FTL doesn't really limit us to this solar system either: generational starships with nuclear pulse propulsion [1] could get us to the next star with around 100 years travel time. Not exactly something we want to start tomorrow, but fairly feasable.
Viable long-term survival strategies on Earth have some pretty hard limits. Even if we master famine, disease, our own worst impulses, and asteroids, there's still the expansion of the Sun. Even if we don't expand beyond our own solar system, the technological advances gained in doing so could be invaluable for maintaining our home planet.
So yeah, I'd rather just focus on developing survival strategies for our rock. But the whole discussion is maybe a bit off topic here too.