They are too dishonest to say such, but their atheism is really a rejection of Christian morality. They believe in personal morality and that is no morality at all.
So the only morality is Christian morality? That's strange. I would think morality would be inherently logical. I don't believe that one can be successful in life without morality. Any student of logic can find morality worthy. It doesn't take the Bible. But I would figure to most Christians (at least to Protestants--I'm ignorant of other sects), morality isn't as important as faith. Sole fide and all that. That's what makes Christianity different from every other religion---you won't be saved by good works alone, but only by accepting Jesus Christ as your savior.