You can actually tweet/write agreement with acts of violence and advocate for it in a general sense in the US. The legal standard is whether that speech is a threat to imminent violence (encouraging violence at a specific place and time): https://en.wikipedia.org/wiki/Brandenburg_v._Ohio

Furthermore, defamation/libel is not covered under criminal law, it’s considered a tort so it would be a civil suit.

So no, not at all like the UK.

EDIT: But yeah sure if you want to try to defend your point, start linking cases to support the claim.