Atheism is inherently nihilistic. If you hold a staunch belief that God doesn’t exist, then you must also concluded that life has no meaning. If you preach atheism, you’ll inevitably produce nihilism.
There’s still room for morality under the banner of atheism and nihilism though, because one could argue that it’s beneficial not to lie, cheat, steal, kill, etc. That it’s more sensible to have a society of cooperation, with rules governing competition.
This is true for most people. But there are some who benefit more from living an amoral life. We know of such people. Some of them become powerful politicians, business leaders, etc. Some of them eventually fall from grace, but many don’t.
Is there any doubt that brutal dictators are either atheists, or theists who believe in a perverse God? Wouldn’t a leader who believes in a loving God be better? Wouldn’t leaving the door open for such a belief be better than keeping the door closed?