The label of Christian is of little value when seeking to understand what it means about the person taking on that label. It doesn’t tell us what that persons moral values or outlook are nor does it really tell us what they believe.
The label itself is an umbrella term or superset of a wide variety of beliefs. Take some examples to highlight this.
Fred Phelps, that hateful bigot of the Westbro Baptist Church who spends his days spewing his hatred of gay people and anyone else who can think of in the name of a tyrant god. This man represents everything that is twisted and cruel about modern Christianity. Is he a Christian? Of course.
John Shelby Spong is a liberal theologian, an academic who talks of compassion and reform. He seeks a move away from theism and an embrace of a shared system of values across all faiths and none. His religion is a hope rather than a certainty and, as far as I know, he doesn’t use his Christianity as the blunt tool to bludgeon others into supporting it. Is he a Christian? Of course.
Joseph Alois Ratzinger, Bishop of Rome and current Pope is another academic. While Spong is liberal and open, Ratzinger is conservative and insular. The recent child rape scandals that have rocked Catholicism have turned his policies into protection of the church. In my view he is a criminal responsible for the continued protection of child molesters from secular justice and he should be tried in a court of human rights. Is he a Christian? Of course.
Rowan Williams is Archbishop of Canterbury and is currently presiding over a near schism within the Church of England. He seems to be a decent enough fellow with liberal views regarding the ordination of women and with the open acceptance of gay clergy but he plays a game of internal politics against other bishops who want the opposite. He is undoubtedly intelligent and articulate and he believes in a literal God rather than Spong’s conceptual god. Is he a Christian? Of course.
When someone announces that they are a Christian which of these models do we most closely associate with them? Are they liberal or conservative? Are they pro-gay or anti-gay? Are they feminist or misogynist? Are they pro-life or pro-choice? Are they hateful bigots or compassionate advocates for equality? Who knows? All we can tell about them from the label is that they believe in some sort of god in a loosely Christians tradition. We don’t know anything more about them than that.
So when someone introduces themselves as a Christian it tells us very little about their views and so cannot, in all fairness, be judged on those views because we don’t know what they are.
The same applies for those who judge atheists based on nothing more than pre-conceived notions.