My understanding of the "modern" point of view is that selection acting at the level of the gene (not the organism or group) is sufficient as a theory. The Selfish Gene and The Extended Phenotype go into this stuff in a lot of detail.

Totally agree with your first sentence though. And even if there is a plausible adaptive function it may have only been adaptive in the past, or might be a side effect of some other adaptive function (see sickle cell anemia), or a host of other possibilities.