Just like anything else foods can get a bad reputation. The thing about reputations is that they can be repaired and scientist are working round the clock to make sure we're not skipping out on foods just because we've heard it through the grapevine that they're bad. Mushrooms, avocados, peanuts, eggs, and coffee [1] top the list of foods with the worst reputations to stop avoiding.

Here are highlights [2] on why you should stop avoiding mushrooms:

• Mushrooms
  Misconception: Mushrooms are a low-calorie food with little nutritional benefit.
  Why they're good for you: They may be 90 percent water and have only 18 calories per cup, but mushrooms are getting serious scientific attention. Laboratory reports and animal studies show that compounds in mushrooms may do everything from bolster immune function to suppress breast and prostate cancers and decrease tumor size. And now, Penn State researchers found that mushrooms, from the humble button to the giant portobello, harbor large amounts of an antioxidant called L-ergothioneine. The scientific buzz is that fungi, for the moment, are the only foods that contain this compound.

Source [3]