re: ESA should just buy and fly an MER...
Oh absolutely it would never happen; as a political scientist, I'm all too aware of the many, many reasons it wouldn't.
In addition to the export and jobs issues, there's also the broader connection to European defense industry -- as with the US, part of the point of space missions is to support cutting edge aerospace and to inspire future generations of scientists and engineers. That's probably even more true for Europe than in the US, since our taxpayers are more willing than Europeans to pay for military R&D directly.