I recall an episode of Star Trek where residents of a planet fought a war with another planet by computer simulated attacks. "Casualties" were selected by the computer and were required to report to disintegration modules to be terminated. I suppose that technology could be adopted by the environmental wackos.
More likely, something like “The Family”, where people are terminated around age 62 or 65. It makes room for the younger ones, eliminates those with memories of a different world and can be held up as saving the environment and health care costs.