That's not how libel law works in the US, or indeed, in the UK. It applies to specific statements of fact about specific people, and does not cover opinions. For libel law to apply, you'd need specific false statements of fact about specific named people that led to damages to those named people, eg, "John Smith has done X, Y, and Z deplorable acts, and someone should kill him", which someone then read and proceeded to kill John Smith. In this case, of course, the conduct would violate a ton of much more serious laws (that is squarely in one of the exceptions to the first amendment, for obvious reasons!), and to the extent that the above conduct did not happen (and as far as I know, it did not) libel law is simply one more of the many laws that don't apply.
Not all things which are against the law are evil. Not all evil things are against the law. Just because you really think something is evil does not mean that if you look hard enough you can find a relevant law.
Consider Zodiac killer's letters or Breivik's manifesto. If copycat killers arise saying they were inspired by reading their letters/manifestos in San Francisco Chronicle/BBC respectively, should these media outlets be closed and/or deplatformed?
This seems to be no different than wanting to ban/close car manufacturers for 2016 Nice truck attack in France, leaving 87 dead.
Those are civil issues, not criminal.