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.
PUFA vs saturated fats come with a lot of caveats. It's generally good advice to avoid saturated fats, but there are only certain conditions in which saturated fats are unhealthy and we don't fully understand those conditions yet. Saturated fats from dairy is even more complicated. It's may not be as bad as other saturated fats.
Recently there are very good studies tracking heart disease progression with extreme accuracy and it is very clear that you can eat high amount of saturated fat for a very long time with zero CVD progression. The mechanism depends on other factors.
Still, personally I think it's good advice to reduce saturated fat until we understand these mechanisms better. Eventually though, I suspect we will find other interventions that eliminate the CVD impacts of saturated fats.
I gotta imagine that margarine with EVO is a clear winner, EVO has several great benefits. Not saying processed seed oils are bad.. I'm not in that camp. Evidence for that idea seems very flimsy.
By all means please caveat away! This is HN after all. I was torn between pithyness and qualifying those statements myself. Obviously there's a lot of interesting variation that's not being captured by population means or the limited subgroups we've studied and I'm excited for us to learn more.
In the meantime, I use butter because it's tastier and for me that's worth it. I don't understand why that's not enough for some people.