[dragonwriter]

What most countries consider libel is free speech in the US, which is why the US standards for libel, especially against public figures, is higher than most other countries.

Specifically, the First Amendment protection of free speech (and the identical rules incorporated against the states by the 14th Amedment) are why, among other impacts:

(1) In the US, falsity is an element of libel, rather than truth being a defense (or, in some foreign jurisdictions, not even necessarily being defense always.)

(2) In the US, libel against public figures (either in general, or limited purpose public figures within the scope in which they are public figures), requires the plaintiff to prove actual malice on top of the elements of libel that apply in other cases.