You can't be serious. We've gone 2/3 of the way to ruining our own planet and now you want us to start wrecking another one as well? What's the point of using unimaginable resources and effort transforming Mars into a copy of earth when we're already messing up the earth? We'd just mess up Mars too. Given the difficulties, do you seriously think this would alleviate overcrowding on earth? And even if it did help slightly with overcrowding/resources exhaustion here, we'd only be putting our problems off for a short while until we'd used up Mars as well.
We need to sort out these problems of population/ecology/resource usage right here on Earth before we try to colonize anywhere else. Anything else is just escapism - trying to avoid facing up to our problems.