This is idealistic in the extreme. I think it could be easily argued that for our own sake and that of the environment we live in, humans could use more natural attrition, not less.
If we get to a point where large portions of our population are no longer oppressed or in poverty, where horrendous wars are largely a thing of the past, and we are already managing our population and environment in a healthy way -- then I'll be in your camp but right now we're doing exactly none of those things so, uh, no way getting rid of death is a good idea IMO.
What's your evidence that more attrition will create a greater society? If anything, greater longevity of people would allow for the accrual of more knowledge and wisdom. Living longer gives you a better long-term perspective. Give people a direct reason to care about what the environment will be like 150 years from now and maybe they'll care more about the CO2 they're putting out.
but right now
None of this is right now. We're right at the infancy of genetic manipulation. Even with the accelerating rate of technology growth, we won't understand our biology at a genetic level enough to be able to manipulate it in an everyday way for at least 50 to 150 years.
It isn't a great leap to think that if we learn to alter our bodies at the nano/genetic level that we can handle our own evolution.