I think there can be some middle ground. Obviously speculation is pushing up both rent prices and the cost/availability of houses to buy. There are some interesting options, I like the idea to only allow residential property to be bought by physical persons - regardless of whether that's for living in it or as an investment it would put a damper on prices sky-rocketing.

Corporations trust funds and so on can still go mad on commercial property. Offices, malls and warehouse are not a necessity and let the market decide, I think that could be a win win. Feasibility of this in various countries would obviously vary but I'm sure something can be done.

I've also seen suggestions aroud limiting the number of properties one can buy/own. Interesting but more complicated to enforce and IMO not needed.