Letters and punctuation are not icons at all. They are symbols. Icons are images, i.e. likenesses of concrete or abstract objects which they refer to. Letters have no meaning on their own, they represent sounds, which differ based on language (e.g. c sound like see, chee, key, gee, that &c in different languages) or its position in a word (caps, ace, click).

And if its not an abuse of fonts to use them as icon packs, its an abuse of the users who wants to use their bandwidth for better things (e.g. cat gifs). I have them disabled and my day is full of fun: What this "f" means? What happens when I click "ff" or "p" or what not? And some are kind enough to provide alt texts, which is soooo helpful: https://imgur.com/cHdSxcO