> If you drive towards a wall and you're accelerating and all you're doing is slowing the rate of acceleration you're still going to run into the wall at terminal velocity.

To complete your metaphor and make it more accurate: we don't know exactly how far away the wall is. Reducing acceleration (emissions) is good unambiguously. If we reduce them fast enough, maybe our seatbelt and airbags will make the crash survivable.

> Our ecosystem doesn't care whether we tried really hard and if we were really good citizens or whether we did nothing

Yes, it absolutely does "care". It's not a black and white issue. Each fractional degree more of temperature increase causes dramatically more serious change to the environment. Every possible reduction is valuable.