Zoning has its uses, but the core of your argument seem to rest on a belief that cities should not rezone because it violates some agreement. I am not aware of

Zoning has its uses, but the core of your argument seem to rest on a belief that cities should not rezone because it violates some agreement. I am not aware of any such agreement in law or moral codes, although I do appreciate the sentimental attachment to what was when things inevitably change. Quite to the contrary rezoning is a normal way for cities to respond to changes in needs. You do however have a right to decide over your own land and to negotiate with other interests on changes to zoning rules, and I wholeheartedly support that. Considering that land value has generally risen with density in western society and the economic drivers denser cities have become, I do not think your argument that higher density reduces monetary land value holds up to scrutiny.