Atheists are not "quite diverse", nor do they "likely" skew socially liberal.
Atheists, and those without religion are naturally, overwhelmingly liberal, and strongly, anti-conservative.
We're not talking about people who are exclusively self-described atheists - who are relatively rare - but people who say they don't have a religion.
There are plenty of people like that who do not hold strong views on religion.
There are plenty of fiscally conservative independent/libertarian types who are not religious.