Companies have been selling harmful products for centuries and continue to do so. The only difference now is that where there is sufficient evidence they are supposed to warn consumers of known or suspected harms - see e.g. tobacco and nicotine products, alcohol, asbestos, energy drinks, fire retardants, carcinogens, some artificial colours as just a few.
However, large industries and companies have enormous, bullish litigation departments and lobby groups which exist to make sure that their sales interests aren’t damaged, as do their insurers to ensure they don’t have to acknowledge a harm and pay out. I work in insurance: I know how hard industry works to defend the indefensible to protect financial interests.
In general, companies know about the emerging risks and harms of their products long before unequivocal evidence forces them to acknowledge it and either post warnings to consumers or remove a product from sale.
That consumers buy products which later turn out to be harmful isn’t because consumers are vain or stupid or unintelligent. It’s because consumers don’t stand a chance against these companies. In the example of non-industrial talc exposure, parents were encouraged for decades to use J&J talc as part of their baby’s essential routine for skin health and protection. There were even huge deals done with the healthcare industry in the US to promote it. That this has turned out to have been probably not such a good idea after all doesn’t speak to the stupidity of those parents but more to the trust that people had decades ago (and indeed it seems still today - several people on this thread have stated the belief that companies aren’t allowed to knowingly sell harmful products, easily disproved) for what large companies told them, and in advertising as truth.