Residential land is far too valuable for someone to ever propose an oil refinery or manufacturing on it. The separation between industrial uses and residential

Residential land is far too valuable for someone to ever propose an oil refinery or manufacturing on it. The separation between industrial uses and residential uses were already underway before residential zoning was invented, and there is no reason to believe single family residential - which is a particular and extremely restrictive form of residential zoning - is necessary to enforce this kind of basic planning distinction.