Replying to Natural/Organic vs. Manmade/Chemical

Where did the whole bias that everything natural must be good for you, and any chemical is bad for you. I'm sure a lot of people are going to disagree with me, but people have said to me a bunch of times when trying to explain why they're taking some all natural organic nutrition supplement that "It's natural, it can't be bad for you" There is so much natural shit out there that is in fact not good for you, but people will go for that over a manmade drug that was tailor-made for the specific ailment. Feel free to agree, disagree and discuss, but it just seems to me that people are too caught up in words like natural and organic in the things they buy.