Dualists are people who believe that reality as we experience it is fundamentally different from reality as it actually is, which we can’t know (that is, we can’t know reality as it actually is). In the west this was popular before Socrates and after Descartes. A familiar example of modern dualists are Materialists who believe that there is nothing besides matter and therefore there is no such thing as free will. When it comes to actually living, they basically just shrug their shoulders and make decisions anyway because we experience free will, even if in reality it’s a complete illusion. (They’re wrong about this, of course, but I’m not going to bother with any further disclaimers to that effect; I trust you, dear reader, to supply the rest yourself.)
And there’s a curious thing about dualists: they usually believe that there is some link between reality as it actually is and the world of perception which we (supposedly) can’t escape. Most of them are more 1.95ists than true dualists. What’s significant about this is that this link is a source of power: it’s possible to use this link to modify the underlying reality in ways that affect the world of perception.
To keep with the example of Materialists (which New Atheists almost universally are), they believe that things like love, loyalty, curiosity, wonder, awe, compassion and so on are all the epiphenomena (that is, an accidental manifestation, analogous to a symptom) of base instincts which we have because they resulted in our ancestors producing us. This is not to say that the epiphenomena are themselves necessarily of any value, but the instincts which produce them must have been of some evolutionary benefit. To try to interact with these epiphenomena may be unavoidable, but it is not very likely to accomplish much since none of them are real. By contrast, there does exist an ability to probe reality. It’s limited, difficult, and tentative; and its name is science. The point is not, of course, to improve the evolutionary benefit. Just as evolution does not “care” about the individual, the individual does not care about evolution. The point is to understand the mechanisms which evolution produced in order to change those mechanisms into ones which are more convenient. A good example of this is anti-depressant medications. (Or perhaps it would be if anti-depressants were more effective.)
Even those who suffer greatly from clinical depression are often hesitant to take anti-depressant medications because psychoactive drugs are terrifying. There is of course the possibility that they won’t work in dangerous ways—there are anti-depressants whose common side-effects include frequent thoughts of suicide—but the biggest fear is that the anti-depressants would work but turn the person into somebody else. This is not really a concern for the materialist because who he is is a mere epiphenomenon, and its only value is in being happy. If the medication changes him, all that was lost was an illusion anyway. (I should note that when this is practical rather than theoretical, Materialists may well be hesitant because they know on some level that Materialism isn’t true.)
This is why Materialism goes so well with recreational drug use. Caution is of course still warranted for the heavy-duty drugs like cocaine and heroin which can destroy one’s life, but it is very compatible with non-addictive drugs like marijuana, LSD, and endorphin stimulation through promiscuous sex. The main reason to avoid these safer drugs is that they falsify one’s sense of the world and take one further away from reality and hence from the true source of happiness. They’re not just wastes of time but counter-productive because they distort one’s view of reality and pull one further away from the truth. Of course a single, low-dosage usage of such drugs is not likely to have much of an effect (ignoring quality control issues) and I don’t mean to suggest that a person who’s had a single puff on a reefer stick is doomed and bereft of hope. But this is the effect of such drugs; they are chemical lies which take a person further away from sanctity and therefore from happiness.
The situation is radically different for a Materialist, however. First, they start off massively disconnected from reality, so within their worldview their connection to itreality (more-or-less) can’t be diminished. Second, there is no real happiness which is possible, so there is nothing to lose by telling oneself pleasing lies. Happiness is itself just an accidental manifestation of underlying chemical processes in the brain, and all high-level explanations which we have for happiness are illusions, so messing with the chemistry of the brain to produce happiness is not only more reliable, it is in fact more real. Not that being more real is a virtue for the Materialist, but the argument—using drugs recreationally divorces the user from reality—will not even make sense to a Materialist.
This is, incidentally, why one runs into the oddity of the evangelical atheist. If God is dead then clearly nothing matters. Even if nothing matters in theory, however, human beings don’t cease to be human beings merely because they believe they are only flesh robots, and as Aristotle observed all men desire to be happy. The significant difference in effectiveness between trying to achieve happiness by dealing with the world according to its epiphenomena (duty, honor, morality, etc) and dealing with it as it is (scientific fun drugs) is so stark that they are moved by pity to try to spread the word to live according to the latter and not the former.