I use many carbon steel and cast iron cookware, but I agree your point. Just because something has been used for a long time, it only shows that it has no acute effect, but it cannot prove it has no chronic effect. I think the iron part is not likely the concern because we do have a decent understand iron. The effect of the “seasoned” layer (polymerized oil/fat) is less known.
However, at the end, we can question almost all cookware materials like stainless steel, carbon steel, copper, Teflon and of course aluminum… I guess glass cookware is probably the known to be truly inert.
