I thought that, too. I also barely remember a set of studies placing the incidences much higher across generations than the number Saletan uses, although it was for cousin marriage in Iraq (among a Kurdish subgroup). The more same family cousin marriages across multiple generations, the more possibility of defects. It's like the inbreeding of the EUropean royal families- it took a while for the weaknesses to manifest, but when they did... I think we need the meta analysis of the numbers before even thinking about it.

I have a feeling this blurb was too small and the data too great to grab the nuances.

I know that the possibility rate of defeects for birth at 48 and 50 are very different than those for 40-43. You can not conflate the risk of giving birth "in the forties" this way. Statisticians and OBs are wringing hands right now.