Militant atheists don't believe in nothing, of course. In place of religion they have politics, today enrobed in the vestments of "progressivism." They have their symbols, like the little "Darwin Fish" car ornaments and the "We have fossils--We win!" bumper stickers. These serve to proclaim their beliefs to the world just as the "Jesus Fish" ornaments and "Jesus Saves" bumper mottoes do.
The odd (from a logical perspective) thing is that these self-proclaimed scientific progressives display a marked reluctance to apply evolutionary reasoning to their own policies. In the writings of Dawkins (The God Delusion), Hitchens (God Is Not Great) and other prophets of non-belief there is scathing contempt for anyone who advocates for the intelligent design of physical and biological systems. And yet, the same people believe absolutely in the intelligent design of social and economic systems. That is, so long as they and their friends are the designers.* Both social behavior and the design, production, and delivery of goods and services are to be governed by a "higher power." Whether that power is royalty, the Politburo, the Department of Commerce or the EEOC, it's all the same. Call it divine right, fascism, socialism, communism, environmentalism or whatever, it all comes down to the control of society by a central authority. It is socioeconomic Lysenkoism,** an orthodoxy forcing itself on the rest of us, justified by pseudoscience.
If one really took the principles of evolution seriously, what policies would make sense? In biology, random variation and selective retention is the principle explaining the adaptation of organic life to environments, including the appearance of entirely new kinds of organisms. By analogy, any socioeconomic system seeking to optimize adaptation and growth must maximize the diversity of goods, services, ideas, and so forth so that those useful and satisfying to people would be chosen and those less so would not. In consumer products, education, housing, transportation, and so on, society should foster innovation---that is, variation--on which selective retention would work. The same goes for modes of life, philosophies, arts, entertainment and the like.
Darwin would recognize this idea. So would Adam Smith. Or Thomas Jefferson. Economically, it's called "free market capitalism." Socially, it's simply called "freedom," as in the Bill of Rights. Intellectually, it's called the "marketplace of ideas," what universities were supposed to be and so seldom are.***
The next time you're harangued by a militant atheist or some other progressive type you might ask them why they deny the validity of evolution by natural selection. Then you can explain, as above. You won't convert them, because ideologies are emotional, not reasoned.
But it's fun to watch them sputter and fume, and at the very least they'll quit annoying you.
* Academics are particularly prone to this fallacy.
** If you don't know about this, you really, really should. Start here:
*** See "The New Plantation," if you haven't already.