I would be inclined to say that a viewpoint-neutral rule prohibiting vulgarities or epithets might well be constitutional, since the ballot is a state-created limited public forum.Well, there is no such rule. There was a ruling, and it most certainly was not viewpoint-neutral: It was directly viewpoint-discriminatory.
Volokh then refers us to a federal case from New York where the dispute was over exceeding the maximum number of letters in a ballot message, yet the "epithet" was allowed to stand. Not helpful.
Further demerit points assessed against Prof. Volokh for egregiously conclusion-assuming use of the word "since." Final grade: D.
Surely by the time they've reached voting age folks have had more than ample opportunity to get their delicate sensibilities assaulted. I know some 13-year-olds who read The Onion (and get the jokes).