Earlier quoted context omitted.
So what about all the characters in Unicode that map to different phonemes or words in different languages? For example, Latin letters are sometimes used for different phonemes in different languages (and dialects, and applications like romanization), and Han logograms are sometimes used for different words/morphemes in different languages. How is that different from "picture of crap" mapping to different specific wo…
The distinction between normal language and graphical representation is the same as what is clipart and what is a official part of a language. Is poo a letter? No. Is A a letter? Yes. Fonts are not a clipart gallery and not a place for some committee to dump little pictures. If you want to show me a snowmen over the internet, use an image! Certainly people can understand an image of a snowmen.
Of course these are "official part of a language". But why? Under whose authority? You could cite "actual usage", but many of the emoji in Unicode certainly have seen actual usage for 10+ years in East Asia, so they qualify. And many of the letters in Unicode were in fact designed by committee prior to mass adoption by an actual population (for example the Hangul alphabet), so a lot of scripts already in Unicode originally didn't meet that barrier.
* = Letters vs. characters: Elements of alphabets are referred to as letters. Alphabets are graphical representations of phonemes, but many other writing systems encode syllables (syllabaries, like the Japanese kana), morphemes or words (logographies) instead. Unicode contains examples of all of these, and thus not just letters. So we want to talk about characters instead.