Without a light, most drivers will - truthfully or not - claim they did not see you if you get hit. Most people who read or saw the news would be inclined to agree.
There is a huge variety of small and unobtrusive lights out there going for minimal cost. If someone chooses to ride without a light, they are absolutely asking for trouble, and very few people will pity them. There is just no excuse ever to go without one when the benefits far exceed the costs.