I think that one problem that so many Christians (and other religious people) have is the idea that only followers of their faith are moral people. Just because someone is agnostic, or even atheist, does not mean that they do not live by a code of ethics or are good, caring people. We did not corner the market on goodness. There is a chance that we feel that these things a non-Christian wants is always immoral when in fact it may be more about “self-determination.”
However, in the West, the morality that exists, (or rather what’s left of it) is derived from Christianity. Specifically, it is derived from Catholicism as Catholicism was the predominant influence on our culture for some 1500 hundred years.
The atheists and agnostics you meet in the West often espouse and live by virtues which are largely derived from Christianity. This is because the Christian ethic pervades our society. It is the background ethic, so much so that people take many of these ideas for granted.
These include ideas like: individual human beings are important; life is valuable; individuals have the right to property; children are people and are valuable, etc.
These ideas are often taken as self-evident. However, they are not. In many cultures of the world they never evolved. Individuals were always seen as subordinate to the group or tribe. Children had little or no worth.
As just one example, think of Hinduism. Hinduism has many positive aspects. But a very negative aspect is its absence of any importance of the individual. People are not seen as inherently deserving of dignity simply because they are people. Traditionally, an entire Caste of people is deemed the “Untouchables” and they are shunned by everyone. To enter this Caste, one has simply to be born to parents who are in it.
If they were truly self-evident, all cultures would believe the ideas listed previously. My point is that those ideas are largely derived from Judeo-Christian philosophy. I am not claiming that they are unique to this philosophy, but in our culture this is their source.
Atheists immersed in our culture have absorbed these ideas and frequently don’t realize their ultimate source. Having been taught them since birth, they have the feeling of plainness which makes them appear self-evident. Such a thing could not be further from the truth.
There is no rational code derived from Atheism or Agnosticism which would lead to such ideas. History declares this. Simply look at those in the past who have acted in accord in with the thinking of atheism. This includes men like Lenin, Stalin, Mao, Pol Pot and their minions.
Ultimately, goodness as we know it comes from the Church. The stamp the Church has made on our culture is so deep, that those who live within it hold many of its moral positions without realizing that they do. They simply take them for granted.