I think the problem isn't the population being in debt, because, as you mention, in China, most people pay cash as debt is anathema for most indivs. On the other hand, one or the main forces behind the construction is local government revenue. Local govt's raise funds through land leasing and selling. In order to remain solvent they enter into these real estate deals, if they are successful, they do well, if things go south, they are in debt --so there is the danger lots of local (CN) gov'ts being insolvent.