i dont agree with the statement. before i say anything else, i would want to mention that i have no idea exactly how the API's (the vits and extracts ect you've mentioned) are produced nor the production processes.

so assuming that what you've mentioned is correct, i.e. the manufacturing of the API's mentioned uses the range of seemingly nasty substances in the processes, it does not mean that the substances are present in the final product. this would be the case as it is a legal requirement to test for toxic substances and levels are actively monitored. furthermore, the stuff you are taking would be well defined. i.e. if you are taking 100mg of something, you are sure to get that 100mg of something. (assuming you are not taking some cowboy branded supplement )

so as far as supplementing is concern, the clue would be in the word 'supplement' you are not replacing a 'proper' source. you are topping up somehting that a person is lacking or in not taking enough

but when you compared to the 'natural' herbal 'supplements', there is no agreed method on extraction nor the knowledge of what is the actual active ingredient. so the extract would contain 1001 chemicals and as mentioned by a previous post, natural dont mean safe. there are plenty of herbal products that interacts with medications which even within a same type of hebal plant, effects are very different in each person.