Not having dug deep into this subject, I think the first sentence is misleading. The way I think about it is in terms of exposure. Not everyone can tolerate the same amount of exposure to the sun at any given time. Overexposure to the sun can lead to cell/dna damage that can contribute to cancer. This is not to say the sun in a vacuum is to be avoided. People with fair skin should gradually increase the time they spend in the sun to make sure their skin can adapt to the stimulus (sunlight) without getting harmed (burnt).
Discussion
Fair point about the first sentence. More accurately I could’ve said full spectrum sunlight doesn’t cause melanoma. There is more nuance to your cell/dna damage claim. Including melatonin. (No, I didn’t mean melanin.) A cancer contribution pathway would likely involve at least of handful of other dysregulations, some caused by lots of artificial light at night. 
Interesting about melatonin.
That aside, overexposure can lead to bad outcomes even if you’re healthy otherwise.
I think of it the same as exercise. There is an effective dose. Too much stimulus will have more side effects than benefits.