Too much sun exposure is definitely bad, because it increases likelihood of skin cancer. Moderation is the key.
My favorite quip regarding this statistical effect is the observation that the cyanide diet is very effective at reducing deaths due to cardiovascular disease (cyanide kills you much faster, so winds up hogging all the credit).
To avoid the mistake, insist on seeing all cause mortality numbers.
you can look at the epidemic of myopia as a related indicator that kids especially are not outside enough
so this whole safetyism nagging about melanoma is ridiculous when they can just go to regular dermatologist screenings and avoid sunburns