I'm going to have to go with the lead-is-bad side here.
There is archaeological evidence and some speculation that a lead coating inside heating vessels was used in Ancient Rome for the preparation of a warm alcoholic drink for the purpose of leaching the lead out into the heated alcohol, sweetening it. This was the suspected cause of, shall we say, behavioural irregularities among some of the ruling elite.
To put it plainly, the elite Romans who liked a bit of lead mixed in with their mulled whatever gave themselves severe lead poisoning. The leading Romans became too stupid, and too mentally unstable, to properly conduct their affairs. The barbarians probably rang the buzzer and had the gates opened for them. (I know, there were no buzzers).
Lead is bad. High levels of different types of heavy metals in the body are bad. High levels of metals we are only supposed to have a little bit of in our system can displace metals we need, causing physical and mental symptoms, and death. This is not speculation or opinion.
Just because a population has lived with lead poisoning for generations doesn't mean that it isn't harming them or slowly destroying their genepool. Past and common practice is a logical fallacy that often crops up on the reactionary conservative side of discussion; just because it was like that in your great-granddaddy's day doesn't mean that its right.
A human being should be able to change a diaper, plan an invasion, butcher a hog, conn a ship, design a building, write a sonnet, balance accounts, build a wall, set a bone, comfort the dying, take orders, give orders, cooperate, act alone, solve equations, analyze a new problem, pitch manure, program a computer, cook a tasty meal, fight efficiently, die gallantly. Specialization is for insects.
-Robert A. Heinlein