Street violence is awful, completely unpredictable and has no rules - they might be armed, they might have hidden accomplices. No martial art is going to replace basic common sense. In most cases an attacker will have already sized up a victim by the victim's lack of awareness.
Martial arts is the final 10% of an overall personal safety model that should have more to do with psychology than it does grappling or punches. I'm not against it in any way. But the single most effective self defense technique is called 'the fence' as developed by Geoff Thompson in the UK.