What has been said about happy unbelievers? I've listened to many sermons, from Jerry Falwell to Tim Keller to Tullian Tchividjian. One common theme is that bad theology, that misapplication of Scripture, can be the direct cause of temporal sadness, even clinical depression. It wouldn't be too hard to find citations from the above pastors' work, and I imagine that every pastor eventually makes the claim.

For example, I just heard a sermon from Tullian that said having a legalistic, reward/punishment view for improving the behavior of your wife only leads to conflict. Here's another similar quote: "Legalism breeds a sense of entitlement that turns us into complainers".

Yet "legalism" may be a fair description of many philosophies and non-Christian religions. And we don't necessarily see a 1:1 correlation between depression and having other religions. I've known nonbelievers, usually immigrants, who have a very cheerful disposition.

Q:What have prominent theologians said about happy nonbelievers? Are they said not to be really happy? Having a short, temporal happiness? Or have they been careful to point out that bad theology causing unhappiness isn't indication lack of good theology dooms one to general unhappiness?
To be sure, unbelievers can live in a certain state of fulfillment (happiness).  However, that fulfillment would be limited to body and soul.  A person may be very healthy and may have a great career, a great family and great relationships.  Christianity would assert that fulfillment in these areas comes as a result of following the teachings of the Bible, whether knowingly or not.  For instance, overindulging the flesh does not lead to fulfillment.

However, from a biblical perspective, we are not merely bodies and souls, but spirits as well.  Just as our bodies need and enjoy and are satisfied with physical things, so too our spirits need and enjoy and are satisfied only within a relationship with God.

It should be noted, though, that many people who have never experienced a relationship with God really do not know or have no experience to understand what they are missing.  Thus, they may feel completely satisfied, having no understanding that there is more to be enjoyed.  

A person who has never tasted ice cream may assume that all that they have is all they could ever hope for.  One stop at Dairy Queen, though, and they realize they were missing out and will never be satisfied again if they have to live without a hot fudge sundae.

So, there is a deeper spiritual fulfillment that can only be found in God that unbelievers do not experience.