General, there's no faulting the logic of your argument, but it's missing any consideration of the real world (the "context" as you describe it). Sure, there is no inherent superiority between qualitative differences in "intelligence" but I'm afraid it might be expecting too much to hope most people will see it that way. Not only that, but how do we react to these qualitative differences (if they exist)? It's much easier to assume that people all have the same capabilities and try to get everyone to fit in than change our society to give all different styles of intelligence (or whatever you call it) equal opportunity at success.

In other words... you say that intelligence measures are biased by context, but the fact is that we live in a certain context. If we could change the context to fit everyone that would be ideal, but that's not easy (although I'm sure we can do better). I think these types of issues are the "freight train" that Saletan is worried about and I think he's right to worry about it.