Plenty of legal businesses too, e.g. Bank of Brazil in Rocinha:

https://goo.gl/maps/pK3K1Lc24fgh7wzv6

When I lived in an affluent part of Rio, I often got my haircut, bought fruit, veg and groceries in the local slum.

Many locals believed the slums were strictly no-go. While some certainly were, many were fine. Rather than build a mental barrier around these places, I find its better to interact.

Common sense, courtesy, some humility are all that are required - that goes for the high brow malls as well as the favelas.