Freud is writing Civilization and its Discontents later in his career from the perspective of a respected and highly-influential man in his own field. The book looks back on his earlier works and pulls threads from many of them, which he weaves into the supporting material for his new theory about civilization and man's happiness. Having reached the level of importance that he has, he does not feel the need to establish the validity of most of this earlier material, assuming that his readership will accept his supporting theories as given.
Freud is also writing from the perspective of someone addressing his colleagues, and he anticipates their potential questions and objections to his central theory. At these points in the book, Freud uses the rhetorical device of changing his perspective to that of his imagined reader, slipping into their voice and raising questions he imagines they might be thinking. He then proceeds to answer these questions.
Freud does not pretend to answer all the questions he raises but leaves many of them open, implying that his readers might find the pursuit of their answers worthwhile. This indicates a certain respect Freud has for his readers, which forms part of his perspective while writing.