Because if I don't control the population things will get ugly... overpopulation will bring disease and conflict and much greater suffering than killing. I try

Because if I don't control the population things will get ugly... overpopulation will bring disease and conflict and much greater suffering than killing. I try to control the population first by taking eggs, but the hens get very unhappy if I take all eggs, so we always leave 3 or 4. That's enough for the population to climb pretty quickly. Also I don't know that your "killing only when necessary for survival" is really a tenable argument. When exactly is it necessary for my survival? When there's a deadly pit-viper in the house, should I kill it for my survival? For our dogs survival (they are at greater risk because they think its their job to attack the snake)? I generally don't kill it, I capture the snake alive and take it away, at not inconsiderable risk to my life. I think that killing to maintain a well-functioning ecosystem is more ethical than a somewhat vague "killing to survive".