> Milder winters will save more lives than will be lost in hotter summers.
Ecological collapse brought on by adding stress to a system already stressed the hell out by decades of rapid change, however, would probably kill a lot more lives than any saved.
Humans' ability to adapt to change will save many more lives, if we allow adaptation to happen. The biggest thing preventing that right now is doomsday rhetoric. Humans have adapted to much bigger changes than this in the past. Our ancestors adapted to the change from Ice Age to interglacial with Stone Age technology. The idea that we somehow cannot adapt to this much smaller change with 21st century technology is laughable.
Ecological collapse brought on by adding stress to a system already stressed the hell out by decades of rapid change, however, would probably kill a lot more lives than any saved.