The argument is that the opportunity cost outweighs the marginal gains.

The original argument (it's linked is that):

* The major manufacturers are already restricting asbestos

* That asbestos contamination is detrimental to cosmetic quality, and therefore manufacturers have a self-interested motivation to meet their claimed safety specifications

* In any case, the most likely sources of contamination are those which were not yet determined to be cancer causing

* Oh, and we should regulate medicinal talc first before cosmetics