Readers deserve the truth.  You are smart enough to make up your own mind - as long as you have real facts to make your assessment.  Fake news sources insult your intelligence, and assume you are not smart enough to use critical thinking skills. 

Fake news destroys credibility. The information you use directly impacts the information you create. If you use fake news to build your argument, not only do you weaken your position, but you make it difficult for people to believe you in the future.

Fake news is harmful.  Purveyors of fake and misleading medical advice like Mercola.com and NaturalNews.com help perpetuate myths like HIV and AIDS aren't related, or that vaccines cause autism.  These sites are heavily visited and their lies are dangerous.

Real news can be beneficial.  Being an informed citizen means understanding what is going on in the world around you. If you are planning on voting in an election, or making a financial or healthcare decision, you need quality information so you can make the best choices.  Fake news will not help you make money or make the world a better place, but real news can.

Fake news is not a synonym for anything you disagree with, so knowing what fake news IS NOT (editorials, partisan publications, etc.) is also essential. 

Adapted from: http://iue.libguides.com/fakenews/index