The history of music is the story of tonality, which came to fruition in the Baroque period with the advent of the even tempered scale. Tonality, or the idea of a pitch center is found in all musical cultures, so why did modern composers discard it?

First, let's define the concept of tonality this way: a perceivable departure point and destination.

From this definition it should be clear that tonality does not need a diatonic or tertian musical language to be manifested. A pitch center (tonality) can be created in a variety of ways divorced from the constraints of a specific language.

The use of the words "departure" and "destination" is important, stating that the music starts at a specific point and is then directed towards a goal. Simple. The opposite of aimless! And that ties in neatly to the idea from the previous post that our mind seek structure and actually require it in some form in order to find things beautiful.*

No goal = lack of purpose = aimless = pointless.

Does a center need to be the same for a whole piece? (Think Schenker). No. A center can shift from phrase to phrase, as long as the feeling of moving towards a goal is kept.

What about pitch hirearchy? I think this is a slightly artificial and arbitrary concept, but one that is based in an audible reality, e.g.: the leading-tone pull towards the tonic, that's an audible reality. But if we use a different language, modal or freely chromatic, then the only rule that applies is that of voice-leading. (Which again brings to mind Gestalt theory.)

Does that mean music should always have a center? If done with purpose, then okay, knock yourself out. Have a ball.

(By the way, the fact that I support tonality as a cor tenet of music composition doesn't mean I am a fan of the Neo-Romantic or minimalist movements.)

So our initial question: why did modern composers discard tonality? Could it be that it was just easier to ignore this central tenet than look for ways to build upon it? Could it be that composers lacked information? Did they have people writing about music cognition and psychology in the early twentieth century? I'll have to check it out.

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* A shape, colour or a sound can be beautiful on its own and doesn't require additional structure to be experienced as beautiful. But as soon as more than one are combined, the mind looks for structure. (Gestalt Theory.)

Beautiful is used in the sense of an aesthetic experience. Superficial ugliness can and often does result in a strong aesthetic experience and is thus "beautiful".