Regarding overpopulation; I dont think it is necessary to just line up a few million people and shoot them. Cut all foreign aid and let the third world kill each other off with their corruption, famine and natural disasters; stop all government-funded healthcare and let the sick die; and halt all immigration from the third world, and overpopulation would begin to take care of itself.
Eugenics should firstly be applied on a voluntary basis: encourage the production of more children among the healthy and the gifted couples. Discourage the reproduction of habitual criminals, the mentally challenged and the sick, those with hereditary diseases, even offer them financial incentives for sterilization. Start sperm/egg banks of selected donors of high IQ for the benefit of the infertile couples and for those who want to bring about improvement of the genetic stock of their future generations.
On the morality: as a nihlist I cannot honestly say that killing low IQs is evil. I only believe in healthy/unhealthy, smart/stupid and advantageous/disadvantageous. Humans are a social animal and we are genetically programmed to advance our species: killing the weak and propelling the strong. If mass death of low IQs leads to more intelliegent, healthy and strong people, and better organized society, and has more positive consequences than negative: then have at it!
But I'm not sure that mass extermination is such a wonderful idea: think of the costs and bureaucracy, Hitler struggled to kill off 6 million Jews. Even the smartest ANUSite would find it next to impossible to exterminate billions of people...