There are no "safe levels of lead", it's toxic as-is and bio-accumulates in the body, which is the main problem. It also doesn't matter in what chemical-compound or what route the lead comes in, it's still toxic as a heavy element.

Why is everything laced with lead then? Well, it's fantastically useful and cheap element, with wide applications... Paint, pipes, bullets, leaded petrol (the absolute worst incident), batteries, radiation-shielding, it was/is on everything. It's entirely a man-made problem.

Except modern day reality is that if we keep using it we'll all die or at least become dummer. This cost is obviously greater than banning/avoiding all uses of lead in the first place. In the science circles they are betting if a some new magic material contains lead, it'll never (or is allowed to) exit the lab.