No, it is not foolishness to dream and even mathematically figure out how to best terraform Mars. It would be foolish to pass up the academic learning processes derived from such an exercise. However, it would be more foolish to actually terraform Mars at the expense of not getting Earth’s air back to normal.
Just setting foot on Mars could cost about as much as it would cost to reverse global warming.
Global powerlines for solar, molten salt reactors for the safest nuclear and cheaper batteries and conservation (for more solar) is already achievable. But that’s not the entire fix.
We need to create new soil by greening entire deserts. Barging water wasted into the seas from all the world’s largest rivers is the trick, hmm, unless we want to employ more nuclear just for massive desalination efforts.
Yes, we need to relearn how to make good soils right here on Earth first (and perhaps grow a continent full of giant sequoias while we’re at it)!