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._OhioFurthermore, 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.
