If there is no God and people act as such, no one can ever be moral or immoral except by their own definition. This would indeed mean that morality can be determined by individual choice since there is no universal standard by which to judge things. So, if you do not accept the existence of God, you do not accept the existence of absolute moral judgments, only those coming from individual morality which can be both transient and situational. By reduction then, the only absolute is that which is legal or illegal and no one is moral or immoral. Unfortunately then, the only reason not to do something is because of legal consequences which can change by the whim of the majority.
For example, when the Muslim Hutus slaughtered over 800,000 Christian Tutsis in the African nation of Rwanda within a 3 year period in the late 90's or early 2000's ( don't remember exactly), it was both legal and moral as they saw it as a just cause by their own definition. Do we see it that way? Probably not. However, who's to say who is right without some sort of absolute moral compass?
I do not judge the morality of a given system of belief by the behavior of it's adherents. I judge it by the claims of it's texts as people are by nature imperfect. I would hope the whole of Christianity would not be judged merely based upon my imperfect life. I would hope instead that people would explore the teachings of Jesus for themselves as He is a much better example and Teacher than I could ever hope to be. All I can do is have the discussion with someone and hope I give accurate information.