When it is necessary. Humans have replaced the apex predators in a lot of places. If population control isn’t done with deer, the population skyrockets, gets out of control, and destroys the ecology, taking several species and the environment with it
But all that applies to humans, and much more so. The harm done by deer overpopulation is completely and utterly dwarfed by the habitat destruction, pollution and climate change that our overpopulation causes. Based on your argumentation, hunting humans for population control is necessary and ethical.
But of course nobody will apply the logic consistently because of how cruel it would be.
Why don’t we implement more humane population control measures for deer, like spaying/neutering? It might have something to do with humans liking the taste of their dead bodies…