Yes, the fact that you couldn't raze and rebuild Somerville does imply that the existing zoning laws are illegitimate.
Proponents of zoning talk about things like reducing congestion and preserving the character of the neighborhood. If you can't exchange like for like these arguments fall flat. Changing the rules of the game after you've won, so to speak, smacks of crony capitalism. Cynically I believe that zoning laws primarily exist to extend property rights over land that a person is unwilling or unable to buy.
Proponents of zoning talk about things like reducing congestion and preserving the character of the neighborhood. If you can't exchange like for like these arguments fall flat. Changing the rules of the game after you've won, so to speak, smacks of crony capitalism. Cynically I believe that zoning laws primarily exist to extend property rights over land that a person is unwilling or unable to buy.