Read an essay “Why I am an atheist?” by Bhagat Singh. Nice article...Good thoughts and very well expressed..For a while I felt as if I read Candide by Voltaire..
But the entire argument in the essay (leaving the personal traits aside) is based on the fact that suffering is inhuman which shouldn't be entertained by God if he really existed. The arguments took its root from logical reasoning with humanity as the theme which essentially is the root of the communist theory (religion is the opium of the masses as Marx said). The definition of happiness here is the logical division of riches and rights.