It's a strange thing, unlit cyclists in an urban environment can usually be seen, there's enough lighting and while I don't condone it (God knows, I did it enough years ago)...it doesn't surprise or bother me generally.
But...unlit country roads I use, I see a guy on a mtb most mornings, no lights, and every time there are converging cars from each direction, you sense the uncertainty from the 50/60mph drivers, the nervousness of the cyclist, he usually gets almost on the verge itself...quite simply he's risking his blooming neck and causing havoc on the road. I see he now wears hi vizier but still no lights. One morning if it's safe to do so I'm going to slow and suggest he get some lights for chrissakes. A few quid for you families peace of mind...it's not too much to ask is it ?
But in general, I think far more cyclist do use lights nowadays, usually pretty effective ones too.