It's queer how out of touch with truth women are. They live in a world of their own, and there has never been anything like it, and never can be. It's too beautiful altogether, and if they were to set it up it would go to pieces before the first sunset. Some confounded fact we men have been living contentedly with ever since the day of creation would start up and knock the whole thing over.
This is Marlow speaking. Psychoanalytically, we might infer that he sees himself, and men by extension, as more mature than women. He implies that men and women have equal access to truth (whatever "truth" is) but that only men can truly understand it; this suggests that he has some sort of experience or innate compatibility with this truth that allows him to see and integrate his life with it. While we might see his view as contemptuous of women, it is interesting that he uses the term "too beautiful" - suggesting that women's views do have qualities to be appreciated and admired, but that they are optimistic. To a practical person this might be seen as distracting and poisonous, though not necessarily by intention. The mention of "knocking the whole thing over" suggests that men are the caretakers of civilization and that their innate ability to harness and understand truth permits women to have their light-hearted views, while keeping them safely away from the proverbial societal tiller.
A feminist interpretation would probably damn this passage as being misogynistic and nearly eugenic in its suggestion that women are actually incapable of understanding reality or taking leadership roles without destroying anything. Modern feminism might also target the fact that Marlow is (probably) talking specifically about Western, white, upperclass women in European societies, but fails to say so. Finally, there may be issue taken with the idea of beauty; Marlow is imparting a subjective standard, purpose and interpretation on other people's actions, and saying that something is "too beautiful" is not a criticism that can be quantified; too beautiful compared to what, and how?