"HOW COULD anything originate out of its opposite? For example, truth out of error? or the Will to Truth out of the will to deception? or the generous deed out of selfishness? or the pure sun-bright vision of the wise man out of covetousness? Such genesis is impossible; whoever dreams of it is a fool, nay, worse than a fool; things of the highest value must have a different origin, an origin of THEIR own—in this transitory, seductive, illusory, paltry world, in this turmoil of delusion and cupidity, they cannot have their source. But rather in the lap of Being, in the intransitory, in the concealed God, in the 'Thing-in-itself—THERE must be their source, and nowhere else!"—This mode of reasoning discloses the typical prejudice by which metaphysicians of all times can be recognized, this mode of valuation is at the back of all their logical procedure; through this "belief" of theirs, they exert themselves for their "knowledge," for something that is in the end solemnly christened "the Truth." The fundamental belief of metaphysicians is THE BELIEF IN ANTITHESES OF VALUES. It never occurred even to the wariest of them to doubt here on the very threshold (where doubt, however, was most necessary); though they had made a solemn vow, "DE OMNIBUS DUBITANDUM." For it may be doubted, firstly, whether antitheses exist at all; and secondly, whether the popular valuations and antitheses of value upon which metaphysicians have set their seal, are not perhaps merely superficial estimates, merely provisional perspectives, besides being probably made from some corner, perhaps from below—"frog perspectives," as it were, to borrow an expression current among painters.First off, he's yelling at everyone who disagrees with him. Second, his disrespect hides his lack of comprehension. Having just finished St. Augustine's Confessions, which might be presumed to be the, err, "antithesis" of BG&E, Nietzsche fails to see that Augustine reasons from not just Scripture, but experience, logic and science as well. This bit: "...in the intransitory, in the concealed God...THERE must be their source, and nowhere else!" is errant nonsense. In fact, no one I've read claims that.
Third, he uses this to launch into a general questioning of the antithesis of good and evil to claim there is only a world of perhaps and maybes. Or something like that. I got tired of being yelled at, so I didn't go much farther. He doesn't even make an effort to address counter-examples that you can come up with pretty quickly. By this, I refer to the Hitler vs. Mother Theresa sort of thing.
Nietzsche was a tormented soul, both physically and psychologically, so he deserves a certain amount of sympathy. I certainly wouldn't want to have been him. Having said that, I'm not quite sure from whence his reputation arises.
Then again, some people think Marx was a genius and keep wanting to put his ideas into practice despite endless streams of failure, so maybe the problem is with us and not with them.