There is significant data suggesting that atheists are indeed different from the general population.
The negative correlation between intelligence and religious belief
This article from The Skeptic as well as
This extensive, recent study confirmed this in more detail, noting:
lower percentages holding religious beliefs among intelligence elites compared with the general population
a decline of religious belief with age among children and adolescents as their cognitive abilities increase
a decline of religious belief during the course of the twentieth century as the intelligence of populations has increased
Atheism & Morality
“In studies that looked at readiness to help or honesty, it was atheists that distinguished themselves, not the religious. Early in the twentieth century, a survey of 2,000 associates of the YMCA found that those identifying themselves as atheists or agnostics were more willing to help the poor than those who called themselves religious” (The Cambridge Companion to Atheism 2007).
Atheism & Society
Atheists are more likely to hold more liberal political views, and they likely to be more tolerant of others
A recent study on secularization worldwide found that the less religious populations were likely to have higher levels of societal and individual security in any society