Among those who have witnessed the increasing weakness of the Neo-Darwinian model of origins and development to explain biological life, the question has arisen about why anyone still adheres to this theory, and why, in fact, its supporters use ever shriller voices and even lawsuits to prevent the presentation of opposing ideas. There are actually several answers
1. Neo-Darwinism is an exercise in Procrustean science, where observations and conclusions are forced to fit the theory. In his book, The Structure of Scientific Revolutions, Thomas Kuhn observes that "normal science" is "a strenuous and devoted attempt to force nature into the conceptual boxes supplied by professional education." He says that theory directs the construction of experiments and the observations that reinforce and refine the theory. Physicist Grazia Borrini-Feyerabend opines that "the idea to fit something into what is already there drives the great majority of scientists today" (quoted in Paul Feyerabend, The Tyranny of Science).
2. Relatedly, Daniel Kahneman, in Thinking Fast and Slow, refers to a phenomenon he calls "theory-induced blindness." He says that "once you have accepted a theory and used it as a tool in your thinking, it is extraordinarily difficult to notice its flaws." The good news is that, once you overcome your blindness and reject the theory, it might well seem "not only false but absurd." So I think a second reason that Neo-Darwinism hangs on is that its supporters, under the spell of theory-induced blindness, simply can't see how poorly the evidence matches the claims.
3. Peer pressure. Or, the emperor's new clothes. Prestige, promotions, tenure, grants, and success in the scientific world require conformity of thought about the theory of evolution. If you want a job in any area of science, you'd better give lip service to Darwin. Atheist philosopher Thomas Nagel himself is fed up with the demand for conformity. In his book, Mind and Cosmos: Why the Materialist Neo-Darwinian Conception of Nature Is Almost Certainly False, he writes, "Physico-chemical reductionism in biology is the orthodox view, and any resistance is regarded as not only scientifically but politically incorrect." To Nagel, even though he proposes no alternative explanation for life on earth, "The more details we learn about the chemical basis of life and the intricacy of the genetic code, the more unbelievable the standard historical account becomes." The problem is that "almost everyone in our secular culture has been browbeaten into regarding the reductive research program as sacrosanct, on the ground that anything else would not be science."
4. Neo-Darwinism is a religion, or, if you prefer, a metaphysical ideology. As such, a fundamental article of faith in Neo-Darwinism is that the biological world--and in fact, the entire cosmos--is to be explained by mechanisms and phenomena that decidedly exclude anything or Anyone supernatural. This fact explains the hostility of the Neo-Darwinists to the Intelligent Design theoreticians--they suspect that intelligent design theory has implications of the supernatural. And recall that science has been redefined from "the search for truth and knowledge" to "the search for naturalistic explanations." As geneticist Richard Lewontin says, many scientists are committed to naturalistic explanations of the existence of life because "we have a prior commitment, a commitment to materialism." And, he concludes, "that materialism is absolute, for we cannot allow a Divine Foot in the door" (New York Review of Books).
5. Following from the previous reason is the problem of what Neo-Darwinist theory can be replaced with if the scientific establishment abandons that sinking ship. Returning to Thomas Kuhn, he notes that "once it has achieved the status of paradigm, a scientific theory is declared invalid only if an alternate candidate is available to take its place." And right now, there is no naturalistic, materialistic alternative explanation for the existence of the biological world. All of the "alternative" theories are just flavors of basically Neo-Darwinist evolution--panspermia, hopeful monster, punctuated equilibria.
Ultimately, then, it's a worldview problem. Neo-Darwinism is the creation myth of those who want to keep God away. No amount of evidence, argument, or common sense is likely to displace the theory because the theory is a fundamental, unfalsifiable assumption impervious to evidence against it. It's an article of faith. For these reasons, Neo-Darwinism is likely to continue to be propped up for the foreseeable future.