Don't you think we might have to terraform (to experiment with our only planet) a whole lot less if we manage to reduce, reuse, recycle instead of continue as we do?

I agree that it seems likely that we'll have to do some sort of geo-engineering in the future. But if you mean that as an excuse to not even try and just let future generations undo everything with hopefully better tech and a world in chaos, then I vehemently disagree. I don't even have kids nor plan on ever having any, it's just immoral (and perhaps it's my way of finding purpose in life to help fix a problem humanity is facing).