When it comes to matters of fact, however, they absolutely do not have that duty. Particularly when it comes to technical or scientific matters where it takes somebody with training to speak knowledgably on the subject.
If we're talking about if, say, vaccines cause autism, we need to hear from scientists. That's a scientific issue. We do not need to hear from Jenny McCarthy or Jim fucking Carrey, in the name of giving "both sides." Jim and Jenny don't get a side. They have no background in the subject, and it's one that requires fucking background.
Once this happens, your opinion on medicine doesn't matter.
Sure, they can talk about poisonous vaccines to Oprah or whoever is sitting next to them at the Lakers game all they want. They have freedom of speech. That freedom does not guarantee them a seat on a panel of experts.
Yet, this kind of stupidity happens constantly. You get articles like this one from the Toronto Star, explaining how an investigation revealed how World Trade Center building 7 collapsed:
Scientists with the National Institute of Standards and Technology say their three-year investigation of the collapse determined the demise of WTC 7 was the first time in the world a fire caused the total failure of a modern skyscraper.