You may have to correct my history but weren't modern composition techniques pretty unpopular right away. It isn't like academic composers have been building off each other for decades with few listening and so now their music isn't intelligible. Rather the introduction of atonality, the 'liberation of dissonance' and moving off the diatonic scale were very rapid changes to music which were very alienating.

This is the way it is presented in drama-maximizing popular histories of music, but the reality is -- from a purely musical perspective, not taking into account the socio-political conflicts of the time which often played themselves out in artistic battles -- that the development was quite natural and gradual.

Schoenberg was a controversial composer from the beginning, well before he finally decided to stop writing key signatures in his scores. Works such as Verklärte Nacht that are now considered audience-pleasers were initially received with a great deal of hostility. (My own theory on the reason why the meme of Schoenberg's "inaccessiblity" still persists with respect to his compositions of the latter part of the decade 1900-1910 but not with respect to the earlier part is that the political conflict between the pro- and anti-Schoenberg factions that was in existence in Vienna around 1910 was frozen in time by the World Wars, and so Schoenberg comes down to us in history as "the guy who was stirring up all that trouble in Vienna right before WWI". This affects the way people listen to the music: if they're expecting it to be "inaccessible", they'll have a tendency to find it that way.)

This prompted Adorno to say things like

The dissonances which horrify the public testify to their own condition and it is for this reason alone that they are unbearable for them.

I'm curious what you think of his position, actually.

Continental intellectuals like Adorno tend to engage in a sort of commentary on these things that really is basically a form of poetic literature, and is not really to be taken as rigorous analysis, I don't think. That having been said, I think it can be read basically as agreeing with your point

the emotions contemporary [music] evoke[s] tend to be more complex, and darker or at least bittersweet.

i.e., that the new music was tapping into regions of thought-space that folks weren't used to having music go into. I think this is fair. The Schoenberg school can legitimately be considered a manifestation of the wider "expressionist" movement across the arts, which highlighted the darker sides of human psychology.

However, this isn't necessarily the case for post-Schoenberg music. Come to think of it, it isn't even the case for Schoenberg's later works (his twelve-tone period), which are better described as neoclassical. Though darkness returns in Moses und Aron, there isn't much of it in pieces like the Violin Concerto or Piano Concerto.

So I'm not sure inferential distance is the right metaphor. It seems to me that while the uninstructed listener may not understand the works of modern academics, they likely didn't understand the works of Beethoven either but were still able to enjoy them for emotions they evoked.

As you note in your own case, they can do likewise with contemporary music, if they're open-minded and musical enough.

However, we do have to eventually face the fact that contemporary music is simply of higher bandwidth than earlier music: more information is conveyed per unit time (on average), with less redundancy and reinforcement. One has to get used to this high level of information flow, and the speed and ease with which one gets used to it will depend on one's intelligence and musical background.

Where does like, John Adams fit into this? He seems fairly accessible to the uninstructed.

He was the second president of the United States. :-) Kidding, of course.

I'd put him in a similar category to Williams and Glass (i.e. toward the showbiz side of the continuum), but with perhaps slightly higher artistic aspirations. Maybe like John Harbison or Christopher Rouse, who are also said to be accessible to the uninstructed.