[I'm working on a draft article called When Are Lies Constitutionally Protected?, and I thought I'd serialize it here, since I still have plenty of time to improve it; I'd love to hear your thoughts on it! (You can also read the whole article here; all the posts about it will go into this thread.) I began with a brief discussion of constitutionally unprotected lies, and turn here to constitutionally protected ones.]
Keeping some kinds of lies—especially those about the government, about history, and about science—unpunishable is especially valuable given the frequent difficulty of drawing the line between opinion and factual assertions, exacerbated by the human tendency to draw that line based on our own attitudes towards the merits of the speech. This difficulty has been evident throughout the history of attempts to regulate alleged "fake news."
Consider, for instance, United States v. Cooper, one of the Sedition Act of 1798 cases. Cooper was convicted of false and malicious statements based essentially on these passages in a leaflet:
