The most common argument I hear against religion (as a positive rather than whether or not it's true) is that it's lead to a lot of wars.
I dunno... The cold war, ww2, ww1... None of these major ones were fought over religion, at least not religion defined by specific beliefs about God.
Like... Sure, communism did it's fair share of attacking religion during the cold war, Japan had a state religion promoting it's leader while an axis power, etc. But these weren't the primary causes of the conflict.
I'm relatively secular, but it seems to me that society has just replaced God-based religion with secular institutions that aren't really all that far off from religions.