With over 30,000 different denominations and sects to choose from, Christianity bears no orthodoxy, no consistency and no authority whatsoever. It has hundreds of 'official' denominations who disagree, sometime violently on all foundational tenets of the religion. Given the general level of ignorance people have about the religion they adopt and their propensity for moulding it to be what they want it to be, one could argue that each Christian has their own denomination. We can state confidently, with evidence and reason that Christianity hasn't a clue what it believes or why. Until the Christianity’s can actually internally agree and harmonise what they believe and state why, they all remain a laughably absurd and unsubstantiated proposition to those who do not believe. Your argument is not with atheists, it's with the other 29,999 sects who view your Christianity as a joke. Link.