I just want to say that even though I generally disagree with these objections to donation*, I really love the "You can't just throw nutrients into ecosystem and expect a morally good outcome." bit and will try to remember/save that in the future. It's rather interesting that Malthusianism is completely accepted without comment in ecology and evolution, but seems to be widely hated when brought up in political or social spheres, so maybe phrasing it in ecosystem terms will make people more liable to accept it. Probably be best to introduce the concept that way first before suggesting any policies derived from it.

*Not the objection, but the bit where people conclude "So I'm going to keep my money for myself" rather than "So I'm going to give to a charity to distribute birth control instead". Which to be fair you don't seem to be entirely doing, so you're not actually one of those people.