That isn't what actually happens and you know it, else farmers would be lining up to offer open space contracts as an overlay to their existing uses at a fraction of the purchase price prior to expression of civic interest (note: I didn't say an easement). The very combination of corporate interest with police power attendant to civic enterprise lowers the price to be paid. "Just compensation" it is then no longer. Even the sale of only the development right becomes a weapon asserted against the owner who loses any means to use that right as financial leverage for continuing operations.
For one who claims such sophistication in her economic education, that was an instance of cynical baiting.