It is far better to allow "questionable" speech than to put strict limits on what people can say.
Any argument, good or bad, out in the open can be debated and countered.
And as Roamer I has stated, who gets to decide what is misinformation?
On a number of different websites with liberal and conservatives, people on the left are usually upset that media organs like Fox News or conservative talk radio exist. They're not too subtle about wanting complete control of the public conversation.
And, of course, they're the people behind The (Un)Fairness Doctrine and hate speech laws.