The community also depends on the people living in it - a diversity of the types, and incomes, of people benefits the neighborhood. People churning in and out is harmful -- I'd argue more harmful than the increased property value accounts for.

I don't have a good solution for this. Rent control helps a bit, but has bad externalities. Property ownership helps a lot but any measure to drive up ownership immediately prices out lots of people because it's captured very well by the housing market.