From Rachel Carson - Criticisms of environmentalism and DDT restrictions:

…Biographer Mark Hamilton Lytle believes these estimates unrealistic, even assuming that Carson can be “blamed” for worldwide DDT policies.[78] John Quiggin and Tim Lambert have written that “the most striking feature of the claim against Carson is the ease with which it can be refuted.” DDT was never banned for anti-malarial use,[79] (its ban for agricultural use in the United States in 1972 did not apply outside the US or to anti-malaria spraying;[80] the international treaty that banned most uses of DDT and other organochlorine pesticides — the 2001 Stockholm Convention on Persistent Organic Pollutants — included an exemption for DDT for the use of malaria control until affordable substitutes could be found.[73]) Mass outdoor spraying of DDT was abandoned in poor countries subject to malaria, such as Sri Lanka, in the 1970s and 1980s, not because of government prohibitions, but because the DDT had lost its ability to kill the mosquitoes.[73] (Because of insects very short breeding cycle and large number of offspring, the most resistant insects that survive and pass on their genetic traits to their offspring replace the pesticide-slain insects relatively rapidly. Agricultural spraying of pesticides produces resistance to the pesticide in seven to ten years.[81])

Other defenders point out Carson never actually called for an outright ban on DDT, and part of the argument she made in Silent Spring was that even if DDT and other insecticides had no environmental side effects, their indiscriminate overuse was counter-productive because it would created insect resistance to the pesticide(s), making them (the pesticides) useless in eliminating the target insect populations:

No responsible person contends that insect-borne disease should be ignored. The question that has now urgently presented itself is whether it is either wise or responsible to attack the problem by methods that are rapidly making it worse. The world has heard much of the triumphant war against disease through the control of insect vectors of infection, but it has heard little of the other side of the story—the defeats, the short-lived triumphs that now strongly support the alarming view that the insect enemy has been made actually stronger by our efforts. Even worse, we may have destroyed our very means of fighting.