^ Agreed. It's completely pointless to compare Paris to London.
I think a main interest in residential skyscrapers for now, in the short or medium run is to make the high-end niche of the market more diverse, which could slightly decrease real estate rates in quite a few districts of the central urban area. It's always much better, far more effective to rely on the free market development, diversity and competition than on their regulated and subsidized social housing to put prices under a downward pressure. Everyone knows it, that's just basic economics. Those to turn down that market strategy in Paris simply have no interest in a price decrease, so they're blocking any significant try to relieve the local market.
Another essential interest is to enhance building technologies and standards. High-end skyscrapers would pull them up, while social housing frequently tends to be as cheap as it can be, thus eventually mediocre in every respect.
Finally, more business opportunities in other large cities of the country would obviously help Paris and above all entire France in doing much better. We lack serious challengers at national level. Lyon's temper for instance is yet bad enough by nature, but everything was done in Paris to prevent any province from growing bigger.
Generally speaking, the problem in France is simply that the overall national market has been over regulated,
on purpose -- nothing is done by accident here -- not so much to serve the interests of the people as a whole, but more those of an already established and scared social class desperately trying to protect their feelings of privilege, while the world proves them weak and wrong anyhow.