I'd say there is plenty enough science to say that doing nothing is about the worst alternative for the environment, short of actively destructive options like switching the planet to 100% coal power (or possibly chopping up trees and burning them for power, but we're already doing that!). This is basic stuff as climate science goes.
The best alternative for the environment would very clearly be to cease all CO2 release right this second and put all resources toward sequestering CO2 to bring it close to pre-industrial levels, but that's not remotely practical.
The tricky part comes in balancing what's best for the environment with what's practical for our civilization. Doing nothing (let's say locking power sources at what they are today, because renewable power and electrics would naturally become the cheapest options in under a century otherwise) will certainly hasten the demise of civilization and cause many medium-term and long-term problems so that can't be the best, we can afford to do better. The cost of suffering through those problems will be far greater than whatever we can spend to avoid them in the short term, the only question is what we can afford to spend now and how deep into the diminishing returns we should go.
The "too late" argument relates to milestones like +2C where certain consequences can't be avoided, it certainly doesn't mean that there's no point preventing warming over +2C. It still gets worse with more warming, it's a sliding scale that we've just put artificial markers on. There's no point where we "might as well give up 'cuz it's already broke."