The use of DDT is probably the best example of this and its use in the third world was badly mismanaged. DDT is not dangerous to humans, but it is dangerous to some animals. So if you’re in a rich country where you have malaria under control, clearly you should ban DDT or severely restrict its use.
But our concern about DDT in the early 70s basically meant that most of the developing world restricted their use as well. That was probably an immensely bad judgement because yes, it harms animals like birds, but it also saves human lives. These actions undoubtedly led to many millions of lives lost. So that is one example of where we need to be very careful about what we do.
Banning the agricultural use of DDT and restricting it to be used only against malaria did not cost millions of lives. It saved lives by slowing the development of resistance.
Lomborg does not know what he is talking about.