I think it is. To say that you need to perform some arbitrary action or have some arbitrary prerequisite to be a member of a belief structure is silly. I see it as simply being that you are a leftist if you have leftist ideals. Like, you can argue about the applicability of communist vs anarchist vs socialist, because those relate to organizational structures, but to say you can't label yourself as a leftist for a reason that isn't really related to being a leftist is just moral gatekeeeping.