I don't think it was linked to secularism in particular. It was linked to the very idea of a "modern" nation-state, which is what Ataturk was trying to turn an area of the former Ottoman Empire into, specifically Anatolia. The idea of a nation-state at the time being inextricably linked to a homogenous population all with the same culture, language, etc...self-determination and sovereignty were supposed to be determined by "race" and culture.