Musk's vision is largely misunderstood. It's not meant to "replace" Earth. A colony on Mars is meant to play the role of a "backup drive" in case the worst comes to pass on Earth. Which is frankly not hard to see. Musk, for all his money and wits can't stop nukes from flying and he can't stop the looming climate crisis either. What he can do is perhaps bring the long-shot project of human colonization on other planets closer to reality. Whether he'll succeed or not is hard to say, but it's a fact that this project is a must for our long-term survival as a species. Even if we somehow managed to solve every single problem on our planet tomorrow, we would still be vulnerable to any number of possible mass extinction or civilization-ending events.