If more mouths to feed also means more people to labor and make food, why is there poverty and hunger in highly populated areas?
If this question is referring to why Thanos was wrong, I believe that the argument may be that fewer people does not necessarily mean that the remaining people have double the resources, so the people are not much better off than before. However, as to why there is poverty and hunger in highly populated areas, some economies can not distribute wealth like capitalism can. Also, in developing countries, it can take a while for standards of living to increase. One final reason is that what is true for part is not always true for the whole. Even in wealthy cities, there will likely be people who do not have access to such wealth. Furthermore, some people find it easier to beg and live in poverty off of the kindness of rich people rather than find a job and do manual labor. For them, the benefits of not working out weigh the downsides of poverty.
Great question. Lots of possible answers. I would first ask this question to clarify: Are you saying that poverty and hunger come from population increases? For the sake of argument, I could point to most every area on the Earth where populations have increased, and yet standards of living have increased. Perhaps there is something else that is making those populated areas poor and hungry. Perhaps there is something else making those other populated areas wealthy and fed. Keep showing up to find out!