I'm not saying he wouldn't appreciate the Beatles for what they are -- a fabulous popular group. But the idea that he would consider their songs a more worthy successor to the Eroica symphony than the work of Boulez and Babbitt is pretty ridiculous.

I took Vassar's comment to indicate skepticism as to the value of contemporary academic composers rather than adulation of the Beatles.

To contextualize where he might be coming from:

I personally have a strong appreciation of music and have gotten very little out of most of the contemporary classical pieces that I've heard, e.g. at symphony performances. I know several people who have a strong love of music and who have had the same experience. As such, in absence of further data, it seems to me quite reasonable to have a prior against the notion that a given contemporary composer's work is of aesthetic value to the typical person interested in music. Of course the issue may be a musical analog of inferential distance, but a priori that could be an issue in principle be for any unfamiliar music of sufficiently high Kolmogorov complexity independently of its aesthetic value to humans.

It's unfair to make a confident judgment against such music without making a solid effort to attempt to bridge the hypothetical inferential distance, but I think that Michael Vassar's statement that there's serious room for a lay-person (who has not had the time to go through such a process) to doubt the value of such music.

The situation would be different if there was a very uniform consensus among classical music lovers that the contemporary material is best. As things stand; a whole number of explanations for divergent views as to the value of contemporary music could apply: it could be that the people who don't appreciate it are unsophisticated and/or haven't gone through the work that they would need to in order to appreciate it; it could be that the contemporary academic music world is engaged in a runaway signaling game which is unrelated to aesthetic value; it could be that the phenomenon is explained by neurodiversity; it could be some combination of all three.

Standard heuristics apply. Check whether the most highly regarded people in a field seem to have impressive general intellects. Check whether they can send other costly signals that are intelligible to outsiders. (I'm pretty sure Milton Babbitt can write damn good fugues; Peter Westergaard has written the best book on "tonal" (17th-19th century) theory I know of.) Check whether any people you already regard as impressive are willing to associate with these folks. Etc.

Whatever you think the ultimate value of advanced music is, tests like these should at least be able to convince you that it isn't a hoax.

This sounds quite reasonable.