Every denomination of every religion sits on their branch pointing out things from the book they use as a guide and say "I'm on the right branch over here so come join me." and on some branches people will say "Hey really everyone is just on the same tree and if you just get on this tree anywhere you feel comfortable then you will be OK." I have no interest in climbing the tree and testing the different branches when I can walk on the ground and get someplace.
Every religion says they have the truth and I have investigated some of those claims and then came to the conclusion that life is worth living. So I live. I live my life without any concern for what irrational beings I can not see have to say to me from centuries ago. I don't say they must be all wrong, I'm just saying I have better things to do with the life I know I have and choose not to worry about another life people speculate may be.
I don't mean "Life is worth living" in a suicidal way. I mean this in a "I have more important things to do with my life than climb trees looking for answers" sort of way. I mean it in a life is too short to spend all my time praising things I can't see for things I work for. I mean that I have this life that I know about and I am certain of this life and I wont waste more of my time reading ancient myths that I find are in conflict with my own morality.
To me this is enough of an argument. To me this is the defense of my position as an Atheist, not that I ever feel that it something I should have to defend