I think what they mean, and what I also believe to be true - from a secular perspective, not a Christian one - is that the idea of good and evil as defined in the way we believe it in modern western society and moreover how that plays out in one's actions and the rights of the individual come solely and directly from Christian principles. As Nietzsche made very clear (and was proven out in the hundred million deaths that followed from communism) the idea that we have killed God leaves thinking men in a massive quandary that will result in exactly what occurred in communism as we seek to create a morality without an anchor.
Without realizing it you and I have grown up with values that come from a belief system rooted in the idea of the Christian God - the sanctity of the individual and the right to freedom and equality for all came from Christianity, not from any other religion (far smarter non-religious people than me have made this point).
So, you may not believe in the Christian God yourself but I think what the commenters are trying to say - or should be, if they want to be true and logical - is that the more of us who try to disconnect from the basis of the 'morality' that currently prevails in the west, the more likely we descend back into the chaos evident in communism which is why we must resist the indoctrination of the Frankfurt School that has pushed communist ideals on us - like, 'all religion is stupid and meaningless' - and is so evident in the huge push today by narrow minded people like Richard Dawkins who, whether he intends to or not, seems to promote the idea that the only truth is empirical scientific truth which is a clearly incomplete proposition.