With all due respect, that's a load of shit my friend. Morality isn't necessarily a byproduct of a higher power. Atheists can have and live by a strong sense of right and wrong, just as very religious people can have a very questionable morality. As for your Hitler comment, you are correct that if he believed that he was right there is or was absolutely nothing anyone could do or say to make him believe otherwise. But that doesn't change the fact he was a total dick, and a belief in a god isn't needed to know or prove that.
So is God just a illusion that people use to give meaning to their lives? I'm a Christian who is struggling with doubt. The way I see it, we can't prove that God exists or doesn't exist. (Try and I can guarantee you cannot "prove" it). What we want to believe does not change what is truth. That is what makes faith so hard: how can I fully invest into ideas that I am uncertain of? Especially when they impact how I view the fate of other humans in heaven or hell?
All this being said, a life without God would have purpose if you had the attitude of simply living for what is meaningful to you. The problem I have with investing into that side is the same as above....... what if I'm wrong?