They are Far Left revolutionaries staunchly opposed to liberal democracy.
And its politics are not just negatory — they also aim to adapt “preexisting socialist, anarchist, and communist currents to a sudden need to react to the fascist menace.” Conservatives or even moderate liberals who oppose fascism do not find a warm welcome.
The other key point, which probably isn’t made enough, is that these are revolutionary leftists. They’re not concerned about the fact that fascism targets liberalism. These are self-described revolutionaries. They have no allegiance to liberal democracy, which they believe has failed the marginalized communities they’re defending. They’re anarchists and communists who are way outside the traditional conservative-liberal spectrum.
https://www.vox.com/2017/8/25/16189064/protests-george-floyd-antifa-president-trump
Antifa is anti-government and anti-capitalist, and their methodologies are often perceived as more closely aligned with anarchists than the mainstream left.
https://www.bbc.com/news/world-us-canada-40930831
Driven by a range of political passions — including anticapitalism, environmentalism, and gay and indigenous rights — the diverse collection of anarchists, communists and socialists
https://www.nytimes.com/2017/08/17/us/antifa-left-wing-faction-far-right.html