[learc83]

We kill them, because we have replaced the apex predator in most ecosystems.

There are too few wolves, mountain lions, bobcats, coyotes, and bears to keep the population in check, so we do it.

>so the argument boils down to kill them because they're going to die anyway.

There's more to it than that. Overpopulation will cause damage to more than just deer. One of the biggest is the increase in the deer tick population and the subsequent increase in Lyme disease.

Instead of killing them ourselves, we could try to reintroduce predators, but why would a deer prefer being killed by a mountain lion to being killed by a human?