It isn’t a purity test, it’s a necessary accommodation of the fact that people in the US (and I say this as an American) think that the left ends at progressive liberalism, while everyone else in the world sees progressive liberalism as center-left at best because they acknowledge that ‘the left’ extends quite far past the bounds of Liberalism (the philosophy, not the political leaning), because Liberalism is about individualism and property rights but most people to the left of that are collectivist in some way shape or form.
It isn’t a purity test, it’s a necessary accommodation of the fact that people in the US (and I say this as an American) think that the left ends at progressive liberalism, while everyone else in the world sees progressive liberalism as center-left at best because they acknowledge that ‘the left’ extends quite far past the bounds of Liberalism (the philosophy, not the political leaning), because Liberalism is about individualism and property rights but most people to the left of that are collectivist in some way shape or form.