I think grandparent is not quite so cruel! If apartment buildings count as "commercial" (which they would in the industry lingo, which differs from the SimCity lingo) then we can just quarantine the undesirables away into a bad part of town using our Zoning laws!

Stop zoning out multi-family homes and apartment buildings and this wouldn't be a problem. Believe it or not, there are many low-income people living in cities where these things are allowed, and they're not all renting single family homes.