I would mention that it may actually cause property values to go up for single family homeowners. Reason being a developer would have the ability to buy the whole property and build an apartment building.

Each apartment may cost less than the house that was there before, but the value of property together (land + apartment building + individual units) is sure to cost more than when only a single home was on it.

Condo owners, on the other hand, would see the value of their units decrease with the extra competing supply. This, of course, being one of the benefits of YIMBYism for everyone else (increases affordability).