All new housing projects in SF over 5 units are required to have some apartments - 20% - set aside as affordable housing (some developers do off-site BMR's). All developers must do this so it won't affect property values. This is called Inclusionary Housing and it is a way to provide communities with housing that is affordable to residents who don't make a large salary. These tenants still have to provide money for a down payment. This is not the same thing as Section 8 or public housing. This is simply a way for community members to purchase a home at a more affordable price. When someone owns a home they tend to treat it well. It sounds like your main concern is really about living near individuals who are different from you (teachers, police, young professionals).