I didn't notice ... it reads perfectly naturally to me.

Are long sentences always wrong? Should all sentences contain no more than ten words?

If course not. Good writing requires variation, and is not simply the dolloping, piece by tiny piece, of single pearls of fact.

I have ADHD, and consequently it took me several reads to parse the sentence. It’s a real issue for some people, including myself.

How would you rewrite it so that it was better? It seems perfectly fine to me. It's a single thought, why would it need to be broken up into separate sentences?

“In a world steeped in irrational hatreds which threaten civilization itself, is it not curious that men and women-old and young-detach themselves wholly or partly from the angry current of daily life to devote themselves to the cultivation of beauty, to the extension of knowledge, to the cure of disease, to the amelioration of suffering, just as though fanatics were not simultaneously engaged in spreading pain, ugliness, and suffering?”

I actually think this helps me understand the sentence better. The use of “fact” is not necessary, and an example of a filler word. When I look at the sentence, it isn’t the length of the sentence, but the amount I had to parse. Taking out that word and reworking the sentence slightly made things clear to me.

That's a different kind of reworking than I though you had in mind when you complained of it being a 'run on' sentence.