I still think there's a big difference between saying that someone is "affected by mental retardation", or even saying that someone is "mentally retarded" (I regularly read a blog by a US woman who occasionally refers to her clearly much-loved brother, who has some form of congenital learning disability, as her "retarded brother") so that doesn't cause me as much shock as it once did, at least when it comes from a North American source) and calling someone "a mental retard", though.
I suppose it just came as a huge shock in the middle of an interesting article on breastfeeding.