Is all knowledge useful? If you can't do anything with it..if it changes nothing ..if there is no benefit to it...what's the point of knowing it?

Culture almost by definition relies on the amassing of knowledge including that which is not itself useful for survival or even comfort.

We need the mathematics used by the electrical-engineer to design the plant supplying the electricity to our homes; we need the biology and chemistry studied by the doctor to help him or her cure our illnesses.

Yet what a bland, empty society it would be if we did not also have the musician knowing a minim from a minuet; the writer spending many hours studying so the background to the historical but fictional novel is convincing; the sports champion understanding the rules and finer tactics of the game. How poorer would we be without the oceanographer studying the geology or the zoology of the deep oceans; the astronomer showing us photographs of sublimely beautiful deep-space objects while finding the subtler beauty revealed by the mathematics of the humanly-invisible radiation from those objects. 

And do you not think that those scientists might go home and relax by listening to the music, reading the novel, watching the sports - perhaps even playing music or sports, or writing, as a hobby?  

In its end-point a society devoid of knowledge gained simply for the joy of knowing without obvious, practical purpose, would be a "dead" society, not a living culture. It would be as empty, meaningless, pointless, boring and so indeed non-cultured, as that espoused by ignorami like the Taliban.