No, I do not advocate such a thing, but that was a very popular leftist slogan in the late ’60s and early ’70s. There were buttons, posters, songs, and films.
Take a look at this vintage 1968 film, and see the kids singing “OFF THE PIGS!”

I don’t think anyone was ever prosecuted for using that slogan, seditious as it sounds. That’s because you can’t prosecute someone for the expression of an evil idea — even ferocious advocacy of what would today be called “eliminationist rhetoric.”
Glenn Reynolds is less than confident in the government’s handling of the Hutaree militia case so far, and I can understand why. It may be that they just aren’t saying what they have on these nutcases, but right now it doesn’t look like they have much:

An FBI agent who led the investigation of nine Michigan militia members charged with trying to launch war against the federal government couldn’t recall many details of the two-year probe yesterday during questioning by defense lawyers.
Even the judge who must decide whether to release the nine until trial was puzzled.
“I share the frustrations of the defense team … that she doesn’t know anything,” U.S. District Judge Victoria Roberts said after agent Leslie Larsen confessed she hadn’t reviewed her notes recently and couldn’t remember specific details of the case.

They do have an audio tape of some murderous-sounding anti-police chatter, though:

Assistant U.S. Attorney Ronald Waterstreet played an audiotape of what he said were several militia members talking freely about killing police.
The participants talked over each other, often laughed and made goofy noises and disparaging remarks about law enforcement.

In the legal sense, that’s not much different than a group of Black Panthers sitting around and saying the time has come to off the pigs.
But as we all know, it isn’t eliminationist rhetoric unless it’s coming from the right!