For example if you work all your life, save dilligently etc and then want to retire. You could buy a few appartments and let them out. That would give you an income until you die.

It used to be you could buy an annuity, but to my knowledge those don't pay enough to live on any more.

Like I said, the housing market is pretty broken here, but banning property ownership beyond an arbitrary number isn't the answer. There should be a situation where lots of first time buyers can actually afford to buy a place to live, which isn't the case now, and that's not fair.

But put it another way... if you aren't allowed to own more than two houses, then there's nowhere near as many landlords. Then where would people who want to rent live?

Should house prices and rents be as high as they are now? Certainly not. But are landlords the root of all evil? Also not.