It would reduce "us" and "Them" thinking.
It would promote economic diversity, lift poor and humble the wealthy.
It would eliminate false stereotypes about the poor and wealthy.
It would make neighborhoods less architecturally homogenous/boring.
Lower income and higher income individuals can learn wisdom from each other.
Government has no right to tell me where to live, and what house to live in.
We should focus on taking slum out of people, rather than people out of slums.
More unsafe neighborhoods, due to distributing the higher crime rates around.
Lower quality neighborhoods, due to property neglect by the poor.