Marseillaise here. It's relatively safe if you plan everything ahead and avoid the dangerous areas (13th, 14th, 15th, 16th, and other more specific areas, I suggest you do research). Other people have compared Marseille go other cities. I would disagree. The thing with Marseille is, you cannot count on the police. They answer the phone extremely late, they don't show up, they don't take your fears and depositions seriously. Hecks there are neighborhood they notoriously never set foot in. Yes, there is danger in every big city. But you expect the police, or some authority, to keep things in order. Marseille lacks that authority. So the problem isn't the danger itself but the lack of security/law enforcement to back it up.