Eugene Volokh doesn't understand the dissent here, obviously.
The idea that eminent domain should only be used for public uses and not for private ones is not a statement that if the government wants a mall in a place, that it has to run the mall. Rather, it is a statement that if eminent domain is ever okay, it is only okay for legitimate public uses (e.g. schools, roads, etc.).
To put it in perspective, one may agree that the rules of war are different than the rules of law enforcement. For example, we can't shoot drug dealers on sight or hold them indefinitely as POWs until drug dealing is eliminated. This does not mean that it would be okay to do so if Congress were to declare war on drugs, as "war" is not the appropriate response to drug crime (I'll leave aside the issue of whether or not criminalizing drugs is appropriate).
That is all.