I don't see why slowing population growth requires culling anyone. It requires educating people, in particular women, providing access to contraception and reducing religious meddling. (And no, I don't mean an Albanian-type ban on religion).FWIW, I don't disagree. And I'm down with educating women, providing birth control and reducing religious influence just for their own sakes, so it's not the solution is even a bitter pill to swallow.
But unless we acheive a worldwide "negative" birth rate, that's not actually going to REDUCE the population as the thread title seems to believe we must. It'll just mean that we're INCREASING it slower.
Without immigration Canda's population would be shrinking without having to kill anyone off. When women are given options they choose to have fewer children and are better able to care for the ones they have.