Just because the suburbs don’t have murals doesn’t mean that urban areas that do are dangerous.
I'm not sure if there are murals in the richest neighborhoods (Pacific Heights) or the less dense, more suburban neighborhoods (Sunset, Richmond), but there are murals throughout the dense neighborhoods near downtown. (SOMA, the Mission, Haight, etc.)
https://www.chicago.gov/city/en/depts/dca/supp_info/mural_re...
Palo Alto has street murals scattered around the city in commercial districts and some private homes.
It's two things in the US. It's ghettos, as you say. But more and more it's whites who want to signal that they're "cool" with minority culture, and you see them in economically well off areas.