A salient example, since lead got brought up specifically—
A while ago it occurred to me to wonder how long we’ve known lead is poisonous, since it was so ubiquitous in paint and construction and so many other places until just a few decades ago, so I went on a wiki dive to see when the first alarm bells were sounded about the health hazards of lead.
People have known lead is poisonous since at least Ancient Rome.
It didn’t stop people using it.
Your safety regulations are written in blood, not by accident, not because people didn’t know there were dangers, but because without them, blood is cheap.