The author's point is very different -- it is that happiness can really only be pursued, as opposed to it being possible to obtain and retain happiness in an ever-lasting way -- but that it should be pursued nevertheless.

"huge part of philosophical and religious thought" is sweeping in the extreme.

Take for instance what a Christian would tell you about happiness -- they would hardly be saying the same thing as I mentioned above. Take a Buddhist or a Hindu -- they would probably agree with the first half of the proposition above (happiness cannot be procured permanently) but the entire thrust of those traditions has been (basically) to recognize this fact and give it all up and retire to the caves.