You'll always have differences that will breed conflicts, but he is right in pointing out that religion is one of the main instigators of violence. His reasons to remove religion is not directly because of conflict but because of its limiting effect on rationality.
I'd beg to differ, and say that religion is not the main instigators of violence.
The crusades? At that time, Europe was overpopulated with nobles and did not grow bigger by itself - tensions arose everywhere. Best way to keep the peace? Unite against a common enemy and take his lands (source: Horrible Histories

)!
The First World War? Nationalism. Since everyone appeared to go off to that war with a smile on his face, i'd certainly say that that impaired rational thinking severely.
The Second World War? Also nationalism and quite a bit of racism.
The Korea War? Ideologies, not religion.
Vietnam War? Also ideologies + nationalism. Since soldiers were absolutely convinced that napalming the **** out of villages which possibly might have had some possible connection to the Vietcong would make the world a better place i'd say that quite impaires the rationality.
The Taliban? If they are muslims, they are quite hypocrite about it: It's major source of income is the production and trade of drugs - which is outlawed in Islam. They just want power, the religion thing is just an advertising trick.
Afghanistan war? Revenge.
Iraq war? Resources, justified by nationalism and the whole 'US is awesome, every country should follow the US way' thing.