Living in harmony with the world around us, including our fellow humans, is surely a part of the key to happiness during this life.
For example, if we decide we want to go around sleeping with whomever we choose, perhaps give the odd punch to people who offend us, steal the odd thing that we desire (sadly this kind of lifestyle is not all that rare) - we are bound to be heading eventually towards isolation, loneliness, in some cases guilt.
But to be truly inspired by Christ, I feel we need to move beyond what is simply good for us in this life. Until we drop this attachment to ourselves, how can we really feel connected with Christ?
When we really drop that attachment, then serving God becomes even more important than considerations of the after-life, and so in this sense there is truth in what you say. I also believe living in the hope of the after-life, rather than the expectation, offers us the opportunity to desire God in every moment rather than take Him for granted.
But the humanitarian goodness of an atheist, no matter how altruistic, is ultimately meaningless beyond poetry (if what he/she believes is true).
However, given the actual existence of God, even the goodness of an atheist is far from devoid of meaning, driven as we all our towards compassion and sympathy. In other words, God drives the desire to be good, and we can hop on board freely whether we believe He is driving or not.
That is not a commentary on atheists receiving salvation regardless of belief, that is a judgment far beyond my own opinion. It is simply saying we all share in the instinct to please God whether we know it or not. The fact people may deny that instinct is indicative of free will.
