There can be little doubt that Nietzsche is the most important figure in modern atheism, but you would never know it from reading the current crop of unbelievers, who rarely cite his arguments or even mention him. Today’s atheists cultivate a broad ignorance of the history of the ideas they fervently preach, and there are many reasons why they might prefer that the 19th-century German thinker be consigned to the memory hole. With few exceptions, contemporary atheists are earnest and militant liberals. Awkwardly, Nietzsche pointed out that liberal values derive from Jewish and Christian monotheism, and rejected these values for that very reason. There is no basis – whether in logic or history – for the prevailing notion that atheism and liberalism go together. Illustrating this fact, Nietzsche can only be an embarrassment for atheists today. Worse, they can’t help dimly suspecting they embody precisely the kind of pious freethinker that Nietzsche despised and mocked: loud in their mawkish reverence for humanity, and stridently censorious of any criticism of liberal hopes.
There’s some truth to this. A lot of atheists and agnostics tend to think that, absent any religious convictions, people will drift towards the values of secular liberalism, which acts as a sort of metaphysically neutral position. It’s a bit like the Fukuyama “End of History” argument.
But the values of secular liberalism are something of an aberration, made possible by a lot of philosophical, cultural and economic developments that took place in the west. That isn’t a proof that they’re necessarily wrong; just that they’re far from neutral and require a number of conditions in order to flourish.
Anyway, I’ve yet to see a really convincing atheistic argument for why a particular set of values should be preferred to any other one. They ultimately tend to fall back on a utilitarian defense, except that utilitarianism is not self-justifying, and I find it problematic both as a meta-ethical theory and a prescription for how we should act. Even the ones that profess to avoid utilitarianism generally jump back to it at the last minute.
And if you’re, alternatively, stoically embrace Nietzsche’s outlook, then I really just want to throw a copy of The Abolition of Man at you.