The point I'm trying to make is if you are not religious, then what do you base your moral compass on? The question is how do you know what is good and what is evil?
You say that it is a natural instinct of all humans to know what is right and wrong. You may have the natural instinct to believe it is wrong to murder someone by hitting them over the head with an axe, just so they can steal the money in their wallet. Someone else may have a natural instinct to believe it is morally justified for them to hit someone over the head with an axe and murder them, because they feel they deserve the money that the person has in their wallet and believe that the person is an obstacle that they must overcome so they can take the money that they deserve.
That person may have a natural instinct, but he has no moral or conscience. You're speaking of a specifically deranged individual. Let's face it - Some humans are good and some are not. This will always be a fact of life. But in most case, for so many people, it is a natural instinct not to kill and to have self-control.
Now, why is your subjective opinion on what is morally correct more valid than the person who believes it is right for them to murder someone and steal their belongings?
Why? Maybe because murdering someone and stealing their belongings would create more harm than good. It can also backfire and eventually put me and my life in jeopardy (either be put in jail or have someone kill me to avenge their loved one's death). This is common sense. Humans don't always want trouble.
I'm going to use the same argument I used earlier; you may think that it was wrong for Hitler to murder 6 million Jews, but Hitler and his followers thought it was morally justified to do so. Again, why is your opinion on what is morally correct much more valid than Hitlers?
And pedophilic serial killers enjoy raping little girls before butchering them. It's sick and horrible. Like I said, evil people will always exist in this world. Doesn't mean they are right or have morals. What's your point? And what does this have to do with atheism? It's ironic that you bring up Hitler, considering his deep-rooted Catholicism and the New Testament was a basal inspiration for his Jewish hatred.
I hope you start seeing the dangers that comes with Atheism.
Nihilism. If there is no God or afterlife, then what truly matters? Nothing. In Nihilism, there is no inherit morality. Moral values are accepted depending on one's subjective opinion. It is very easy for an Atheist to fall under Nihilism, and that is where the danger comes from, when people believe that nothing matters they do whatever they feel like doing, or what they instinctively feel like doing. If one instinctively feels that they should murder another person for no reason at all, then how, as an Atheist, can you justify that they are wrong in thinking that? They are acting out on their instinctive moral guidelines, just as you believe all humans do. But why is one particular persons instinctive moral guideline invalid? How do you know that they are not a more evolved human being who sees the truth in reality and understands that nothing matters, why are they wrong and why are you correct? When you get an entire society under an ideology like this, this is when mass destruction and chaos occurs, and there are many examples of this happening throughout history.
No, I frankly do not see any dangers and I'm barely convinced. Yes, there are some evil strains within atheism (state atheism and communism), but there is also such in religion if you check out your history as well. Please take out the log in your eye first before picking on mine, as the saying goes.
Not all atheists should belong to such parties, ideas and such. I'm not a nihilist and I'll be confident enough to tell you that most atheists are not. Look at atheist/agnostic scientists, disease researchers, technological fielders, general innovators, etc. They still provide more good to the world than bad.
P.S. Most atheists know that killing someone is wrong. I'm not sure why you're going on with this. Scratch that. Nearly every human of every religious and cultural background (unless if they're radicals) know that murder is immoral.