> homeowner (me) can't install a duplex addition for a home zoned duplex without turning the front yard into a 4-car parking lot. It doesn't matter that I have one car and could decide to only rent to people with one car, the driveway would need to fit four cars instead of the current two.
Once it is a duplex it is a duplex. You cannot make those assurances for the next homeowner, or the one after that. Even you yourself aren't obliged to stick to your self-imposed rental limitations. Your argument essentially boils down to a hypothetical (that extra cars won't always be needed) but ignores that zoning laws are designed for the common case (that extra cars will scale with number of dwellings).
> if you want to have a home-based day care business, zoning sets a max number of kids that can attend. In California, this is 14 kids. It doesn't matter if your home is 1,500 square feet or 5,000 square feet, whether you're in the middle of downtown SF or in a rural area, or whether you have 2 parking spaces or 20.
So a property not designed to hold a large number of people, isn't allowed to hold a large number of people. That seems reasonable. Just from a fire-safety perspective alone it makes a lot of sense to require custom-built commercial facilities after a certain number of kids.
Plus parking (drop off/pick up), noise, pollution, and so on.
> You should be able to do whatever you want to your property if it doesn't really hurt anyone.
I agree. But all of your examples hurt someone else.