> who got to decide what is extremist or as the study also put it "alternative"?
That's explained in the paper:
> Our list of extremist channels consists of those labeled as white identitarian by Ledwich and Zaitsev (26) (30 channels), white supremacist by Charles (45) (23 channels), alt-right by Ribeiro et al. (24) (37 channels), extremist or hateful by the Center on Extremism at the Anti-Defamation League (16 channels), and those compiled by journalist Aaron Sankin from lists curated by the Southern Poverty Law Center, the Canadian Anti-Hate Network, the Counter Extremism Project, and the white supremacist website Stormfront (157 channels) (46).
That's explained in the paper:
> Our list of extremist channels consists of those labeled as white identitarian by Ledwich and Zaitsev (26) (30 channels), white supremacist by Charles (45) (23 channels), alt-right by Ribeiro et al. (24) (37 channels), extremist or hateful by the Center on Extremism at the Anti-Defamation League (16 channels), and those compiled by journalist Aaron Sankin from lists curated by the Southern Poverty Law Center, the Canadian Anti-Hate Network, the Counter Extremism Project, and the white supremacist website Stormfront (157 channels) (46).