“Liberals”?
Name something more iconic than leftists telling other leftists they’re doing it wrong.
Liberals aren’t leftists.
Edit: to clarify, this is from the Wikipedia entry on left-wing politics:
In modern politics, the term Left typically applies to ideologies and movements to the left of classical liberalism, supporting some degree of democracy in the economic sphere. Today, ideologies such as social liberalism and social democracy are considered to be centre-left, while the Left is typically reserved for movements more critical of capitalism,[9] including the labour movement, socialism, anarchism, communism, Marxism and syndicalism, each of which rose to prominence in the 19th and 20th centuries.[10] In addition, the term left-wing has also been applied to a broad range of culturally liberal social movements,[11] including the civil rights movement, feminist movement, LGBT rights movement, abortion-rights movements, multiculturalism, anti-war movement and environmental movement[12][13] as well as a wide range of political parties.
So some classify liberals as center-left, but center leftists aren’t a thing, and calling them just leftists would be inaccurate.