[digislave]

People can only ask for as much money for houses as people are prepared to pay. It isn't true that speculators can simply drive the price up as high as they want.

If investing in housing is a good way to make money, it is an incentive to build more housing.

Even foreign money could be good. If foreigners pour lots of money into your housing market, you could build lots of cheap houses and sell it to them for lots of money, for example. (not saying you should, just saying foreign investment in housing is not automatically a net loss).