It's not. The tree hugger's observation - supported by a body of research as consistent and coherent and replicable in its findings as all but a couple of investigated matters - is that slowing AGW down by as much as we possibly can will significantly reduce the risk of collapsing human civilization and causing a major global extinction event requiring millions of years to recover. It will also reduce the hardship of dealing with the effects of AGW that fall short of destroying human civilization and most major ecological communities altogether. It's like reducing the risk of a large asteroid impact, if the risk were being created by people building the large asteroid and launching it into a killing orbit in the first place (they needed jobs, see). The tree hugger goal right now is to get people to build only a smaller asteroid, launch it into a less dangerous orbit, and maybe as a last resort figure out how to deflect it or reduce its speed if it looks like it's getting too close. For thousands of years humans managed to live without cars at all. Lots of people still don't travel by car. Lots of people who do don't seem to need head snapping acceleration or eight cylinders of maximally inefficient internal combustion to get to the bar or visit the parents. We know we can live, and live well, without cars - we've done it, and many still do. We don't know whether we can even survive in large numbers, let alone live well, with them. We're only a century or so into the experiment of living with them, and right now it's not looking too good.