Henry George thought that land was our common inheritance, but was in favor of free markets. He did not support rent control. He thought of rent as a fact owing to the value of the location, and the question is not how to make the rent lower. The question is who gets to profit off the fruits of nature.
Rent control, in effect, converts tenants into pseudo-landowners with less fungible rights.
If locations are valuable, and by extension the rents, that is good. But to whom does the rent belong?
If rents are unaffordable, it is because wages are too low and the rent is not shared... which comes back to bargaining power and the overall health of the economy.
Taxing production, for instance, harms economic health.
But allowing speculators to hold the land for ransom creates stagnation, sprawl, and harms the bargaining power of labor... by worsening everyone's best available options for living and working.