Drunks/junkies/mentally ill people shitting, pissing, and vomiting everywhere, while verbally (and sometimes physically) abusing the passers-by.
Noise.
Breathing the stench of exhaust fumes, week-old garbage, and someone else's idea of cooking.
Having no place for your children to sit on the grass without worrying about them finding someone's discarded needle or excrement.
Having no space for gardens, hobbies, or gatherings of family and/or friends.
Bad schools with apathetic parents.
The inability to leave personal property unattended for even a moment.
The need to have extensive home security (bars on windows, etc...)
The much higher likelihood that you or one of your loved ones will be mugged, raped, or killed.
Those are just a few that come to mind.