I mean, in a practical sense, tipping is not optional in the US, at least in the context of sit down restaurants with a server. This is pretty well understood by the vast majority of Americans no matter how loudly people on the internet complain about it.
A lot of the noise as of late has been because as services like Square have become more common for POS payments, they default to including a tip screen. And so people are upset about the view that they’re being “forced” to give tips to types of jobs that have never traditionally been tipped (and apparently they’re too weak willed to just press “no tip”).