“Freedom of speech and freedom of action [is meaningless] without freedom to think. And there is no freedom of thought without doubt.”

When doubt is implied, or preached, Question All authority. 

Skepticism is a good thing.  Being able to express that doubt is liberty.

Doubt, in itself, is hardly the sine qua non of freedom of thought.

Profound doubt, delimited by fear doubt that is, objectively, morbid in character, can so constrain thought as to render free inquiry, which is the true sine qua non of freedom of thought, an impossibility.

Attempting to list an element of importance in describing liberty will always be found lacking. Ron13, Archers and Patrick's comments are spot on in the context given. At natural law, freedom of speech and action are always meaningful with no other qualifier — if for nothing more than to demonstrate the fool's lack of thought.