The government does not originate tort claims of libel. It is there to mediate disputes that citizens bring against each other. Because the next best thing is people committing acts of violence against each other.
The relevant section:
"Criminal libel is rarely prosecuted but exists on the books in many states, and is constitutionally permitted in circumstances essentially identical to those where civil libel liability is constitutional."
Again, this is really beside the point IMO, as I mentioned before. I only brought it up due to being an unreconstituted pedant, unable to help myself.
That's as hyperbolic as my omission is glaring. Yes, there are a few very narrow exceptions made.
I would say, though, that our 1st amendment rights are stronger today than ever.