Wow, this is definitely one of the nicest UV or not to UV conversations yet. I usually see it very heated. (No pun there.)
I do use a UVB and it comes from my own experience. I had a poor little guy who wasn't doing well. After trying everything else on the planet to make him more comfortable, I figured I'd do my own experiment on the classic discussion and bought a cheap zoo med 40W with UVB. Three days later you'd think I gave him a B12 shot! He ate better, moved better, and just seemed to wake up. He was still a very sick gecko come to find out months later, but the difference was enough for me. We dust with a multivitamin powder, calcium dish always available, and have stuck with the UVB light. We have always kept albinos so plenty of hides, but on the other hand our current girl likes to get up in the middle of the afternoon, do a gecko lap or two, get a drink and walk back to a hide. Who knows.
For me personally, that is evidence enough... I won't condemn anyone who doesn't use UV light, I may suggest they try once to see if they do see a difference, especially if they are having problems. I would say, light or no light, multivitamin supplementation is of the highest priority.
Here is my 3 year old, brought up with UVB light, no giant genetics, but she's a full 9 3/4" long and too fat and happy to sit still on the scale anymore:

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0.1 Albino Leo Gecko
0.1 Crested Gecko
1.0 Dear Boyfriend
Departed: Harvey and Spock