Yeah, lack of Vitamin D may or may not be a problem (well, obviously in extreme cases it leads to rickets, but that's rare). But skin cancer unquestionably is a problem, and not infrequently a deadly one. Pick your battles.
Very infrequently. Total death rate per year in the US is something like 900 per 100,000 adults, of which less than 3 are from skin cancer. Heart disease, stroke, other cancers, accidents, are all much bigger.