The Bible teaches that natural man is sinful. The Bible does not insist, however, that natural man is devoid of love or altruistic intent. In Matthew-47 Jesus makes the shocking suggestion that pagans and tax-collectors are loving people. This sentiment might have been challenged by a Jewish audience that was trained to see the Gentiles as a hostile, evil contaminant. Yet it is not difficult to find examples of unbelievers behaving in ways that seem to be loving.
A belief in the depravity of man does not require one to explain away or dismiss every human act of righteousness or love. Rather, depravity means that we can not gain God's righteousness despite our occasional gestures of altruism. Or, as Jesus puts it in Matthew 5, in order to truly be children of God we must “be perfect.”