"The art of not reading is a very important one. It consists in not taking an interest in whatever may be engaging the attention of the general public at any particular time. When some political or ecclesiastical pamphlet, or novel, or poem is making a great commotion, you should remember that he who writes for fools always finds a large public. A precondition for reading good books is not reading bad ones: for life is short."
“Reading is merely a surrogate for thinking for yourself; it means letting someone else direct your thoughts. Many books, moreover, serve merely to show how many ways there are of being wrong, and how far astray you yourself would go if you followed their guidance. You should read only when your own thoughts dry up, which will of course happen frequently enough even to the best heads; but to banish your own thoughts so as to take up a book is a sin against the holy ghost; it is like deserting untrammeled nature to look at a herbarium or engravings of landscapes.”
Incidentally, having quickly scanned some of Schopenhauer's actual writing [0], I found statements such as "women are suited to being nurses and teachers of our earliest childhood precisely because they themselves are childish, silly and short-sighted" and women "are inferior to men in respect of justice, honesty and conscientiousness". If I'd come across these first I'd be very reluctant, rightly or wrongly, to uncritically accept his views on other subjects.
[0] https://www.scribd.com/document/509571816/Schopenhauer-Arthu...
You don't want people to use this sort of criteria to judge arguments. Not just because it's ad hominem, but also for selfish reasons - your opinion that after a "quick scan" one should dismiss Schopenhauer's philosophical thought (his specialty) because he shared a common contemporary opinion on the nature of women (not his specialty) reflects badly on you. If somebody could reasonably dismiss an unrelated argument that you made based on that, your arguments would be ignored regardless of their merit.
Also, people would wonder if you have dismissed all of the writings and discoveries of sexists and racists; if you have then you are obviously uneducated, and if you haven't then your exceptions imply the shape of your own specific racism and sexism. It's a no-win situation for you.
To get a feel for his other work, I read his essay "On Women", which is derogatory and sexist. Female philosophers such as Mary Wollstonecraft had already responded to similar patriarchal sexism (50 years before in her case) and as a philosopher one might have expected Schopenhauer to be familiar with similar intelligent women, and to have acknowledged their existence. His denigration of the capabilities of half the human race does not give me confidence in his other speculations.
[Edit] I also observe that Tolstoy stated "at present I am convinced that Schopenhauer is the greatest genius among men. ... It is the whole world in an incomparably beautiful and clear reflection" [0]. As someone who has slogged through the 27 chapters of philosophy in War and Peace, which are a case study of how to fail to understand how human society actually works, I am reluctant to uncritically accept claims from famous people that someone else is a genius.
[0] https://en.wikipedia.org/wiki/Arthur_Schopenhauer#Influence_...
Yet the quality has gone down when you compare it to, say, 1600's greatest works.
Do you think many people will read Stephen King in 500 years?