Your threat model should be localized. There are plenty of places where the threat of stabbing is low, and should not occupy your mind. There are plenty of places where the threat of stabbing is high, and you should be aware of your surroundings.

Likewise, your threat of being preyed upon on an open AP is dependent on what you're doing on that AP. Surfing HN? Who cares. But if I'm checking my bank account balance or touching sensitive info, I'm absolutely going to fire up a vpn first.