Tom McCormack does a deep dive on the early days of the emoticon:
The conjuring of a voice where there is only actually just a bunch of static text is a huge part of the Magick of good writing. But much of the written word is not trying to be good, in this sense.
The CMU CS bboard could have dictated that all jokes be written with the skill for compression, mimicry, and understatement of James Thurber or S.J. Perelman, but this would have likely betrayed this bboard’s social function, which was to facilitate amusing or pragmatic and low-investment communication among people who seem, for the most part, not to have been humanities majors.
The question of what symbol or symbols can or should substitute for tone of voice was considerably worked over by the CMU CS BBS. What distinguishes Falhman’s from the previous suggestions is that it simultaneously accented the lyrical expressiveness of the word-substitute and added an element of modular variability, two of the most important qualities of the more involved longer-form writing the smiley was intended to obviate.