I'm not sure if "obliterated" is the right word to use, but if making housing affordable means a 20% drop in home prices (which is perhaps not even enough in some places), average Joe existing homeowner is going to run into financial trouble once that happens.
> We can easily build twice as much in high cost areas (with the strongest job markets) with little impact on existing home owners.
If that's the case, then all that new housing will also cost more or less exactly the same as the existing housing stock costs, and the problem will not have been solved yet.