This is not Earth that needs to be fixed, it's human behavior.

Teraformation and space conquest are fassinating topics, but "fixing our behavior to avoid to fuck up the only accessible viable environment we have" is far from deserving only a mere "might be more cost-effective".

But way less fun :)

Or we could, you know, just transfer our consciousness to machines that can easily survive Mars and other environments and start our colonization after declaring ourselves to be Homo-sapiens-machina.