One thing that needs to be addressed, though, is this question (which is often taken for granted): Is it universally a good thing if rents fall?
On the whole, all things considered, high rents are absolutely a bad thing for our economy and our society.
High
demand for real estate is not a bad thing. It is a sign that the local economy is strong and that people want to live here. A drop in rents and asset values that is the product of a fall in demand (like we saw during the Great Recession) would not be good. For example, if the murder rate skyrocketed and Boston streets became unsafe to walk, or if a hurricane decimated the city and wiped out our infrastructure, prices would surely drop as a result of decreased demand. Nobody wants this.
When we talk about the factors that drive our real estate prices and what to do about them, nobody advocates taking steps to decrease demand. The issue to be addressed is that supply is severely constricted. This makes there be fewer properties available than their would be in a true, open market, and so all of the demand must be funneled into this limited set of available properties. The result is that only those with the highest willingness to pay are able to fit in the market and market price rises well above the underlying cost of production.
Some people (entrenched owners) benefit in this situation, but just about everyone else suffers. We all end up having to pay huge amounts of "economic rent" (to be distinguished from real estate rent) as a result of the scarcity. This cost gets cooked into everything you can imagine (not just housing but food, clothing, drinks, etc.) and makes living here uncomfortable for many and completely unaffordable for even more.
There's really no good reason why we should advocate for home and condo values to appreciate, other than the selfish reasons of homeowners. Housing is a highly illiquid, highly leveraged, non-diversified, volatile asset. We should not, as a society, be encouraging people to invest so much of their net worth in such an investment vehicle. If housing were more plentiful and cheaper and seen as less of an investment, we'd all have more available capital to invest in other, more responsible manners.
If these supply restrictions are drawn back (they will never go away completely)
land values would probably increase in the short- to medium-run while the value of built space would decrease (or at least increase more slowly). This is because land is more valuable when more can be built on it, but built space is less valuable when there is more of it in competition. You would not need to worry that construction will suffer as a result of the dropped rents, because rents only drop in the first place as a result of increased construction. This is the big shame of regions like the Bay Area: the great wealth increases that are driving asset values up should lead to building booms that distribute this wealth down the economic ladder. Instead, supply is limited to such a degree that all this wealth gets trapped by existing land owners and doesn't spread to less advantaged groups.
Building values (and rent) will, in an unconstrained market, drop until they reach the cost of construction. City buildings will never be
cheap (steel and glass and concrete are pricey) but they can certainly be cheaper than they are now (without the additional cost of scarcity rent). This is evident in less supply-constrained cities like Chicago, Dallas, Atlanta, Houston, Toronto, Vancouver, etc. where nice, new construction can be had for way less than in Boston, New York, San Francisco, etc.
As for truly poor people, increases in supply still won't make urban living affordable for them. This is because poor people don't have a
housing affordability problem, they have an
everything affordability problem. It's what makes them poor. Just as they can't afford housing they also can't afford food or medicine or energy or any of all sorts of other goods. If they could afford these things at market price, they wouldn't be poor. This is why we have programs such as SNAP and Medicaid to subsidize these necessities for the poor. We'll have to continue doing this for housing as well. The only question is where the burden of the cost for these programs should fall.