This fundamentally misses the problem. Investors are only able to speculate because there is a shortage of housing. They are betting that in the future even more people will want that housing, and they are probably right. The only real solution is to crash the housing market by building more houses in places that people want them. Banning speculation won't solve the problem, and it might actually make the problem worse because we will have even less development that people need. We need to heavily update construction regulations to be more sensible like Tokyo, and we probably need massive amount of direct and indirect public housing investments.