Authority does, in fact, develop legitimacy when turned against oppression (and by extension oppressors). For that reason, leftists frequently correlate bigotry in language with oppression that follows a bigoted division. Leftists internalize a phobia (embodied in a self-restriction) of (from) the language of the oppressor, and this is not to be ashamed of. As the oppression diminishes, so, too, will the sting of the language and the internalization of authority against that language. This is all in keeping with a revolutionary overthrow of the structure of oppression, and fine at that.
What needs to be questioned, however, is the pedantic nature of this phobia when you apply it socially. The fact is that it does nothing to reveal and excise the oppression it seeks to confront. To ban the language of the oppressor is to conceal the identity of the oppressor. It internalizes the sense of oppression on all sides. It fights against the recognition of oppression and in fact insulates oppression.