> However, there are streets in London of very highly priced completed uninhabited houses, which serve as speculation objects and money parking vehicles.
Inhibiting this is another benefit of building even more housing. Speculation only occurs when people expect housing costs to increase or at least stay the same. If you build enough to actually start to lower prices then the speculators will try to get out before they lose their money and thereby put even more housing on the market.
> There are many examples in Germany were newly constructed housing lead to a increase in rents of already existing housing.
This can happen when the shortage is so bad that it's actually harming quality of life in the city, e.g. by making local traffic worse because people who want to be living in the city have to commute in instead.
As you start to relieve the shortage you start to address those problems, which improves quality of life in the city (good), but that makes housing there more valuable and makes people willing to pay more of a premium for it, which increases demand.
That isn't actually a problem -- the demand isn't infinite and improving quality of life is a gain -- it just means you still aren't building enough housing to satisfy the pent up demand.
> Where is the value for the very real people who must leave the city because they can't afford the rising rents, even though they have their work there and their children go to school there?
This is one of the situations where you're almost out of water but the middle ground is a desert. If you don't build more housing, the status quo is untenable. If you only build a little bit it can even get worse. To actually fix it you need to build a lot. Not an infinite amount, not an impossible amount, but quite a large amount. And the status quo if you do nothing is that you die a slow death.
> I just don't think that housing should just be unregulated so the market can have its go at it as if that were the god-given solution to every problem.
Government: <causes problem by imposing unnecessary rules>
Government: We should address this problem by imposing some additional rules.
...
There are things markets are bad at. Matching supply with demand is not one of those things.