Depends who you want to cull I suppose. If you're concerned about it being a natural resources issue then another 3 or 4 billion people in the world's poorest regions with the smallest carbon footprint isn't going to make any difference, but it that was applied to rich industrial nations where unfettered capitalism reigns and over consumption is prevalent, then it would likely finish us off
The very poorest countries (home to 9 percent of the global population) are responsible for just 0.5 percent. This provides a strong indication of the relative sensitivity of global emissions to income versus population. Even several billion additional people in low-income countries — where
fertility rates and population growth is already highest — would leave global emissions almost unchanged. 3 or 4 billion low income individuals would only account for a few percent of global CO2. At the other end of the distribution however, adding only one billion high income individuals would increase global emissions by almost one-third.
https://ourworldindata.org/co2-by-income-region