As a millennial homeowner, living in a historic neighborhood, I am all in favor of taking the empty lots that do still exist in my area, and turning them into h

As a millennial homeowner, living in a historic neighborhood, I am all in favor of taking the empty lots that do still exist in my area, and turning them into high density housing. I watched a 4-5 story building appear on a empty lot just down the street from me. This kind of housing is perfect to help alleviate housing constraints, and offers people the opportunity to live in a walk-able, historic neighborhood and contribute to the community. Why is that a bad thing?