The benefits for who? him? Facebook's investors? influencers and celebrities? or Facebook's users.
TL;DR - Facebook is a "sausage factory", and only a few people know what actually goes on in there. Our collective human history can be used to justify pretty much anything. The chapter that is relevant to my point is that humans are very good at externalizing and abstracting the product for the sake of the customer. The thing with Facebook is that the product and the customer is the same: [two different sets of] people.
To your question, "Otherwise how could he look at himself in the mirror?": What do you use a mirror for that cannot be replaced or overcome with sufficient wealth?
=== The Long; Do Read
Even at the risk of drawing an incomplete, yet horrific analogy, I'll do so anyway. Facebook's users are product correct? Another product consumed by many people is meat. Most meat is prepared in slaughterhouses from animals bred and grown in factory farms for slaughter. There are a lot of procedures that are followed to make the extraction and sale of meat as economically profitable as possible. I don't know of all of them, but here are a few that I do know of
1) Feeding animals hormones to make them grow faster: https://en.wikipedia.org/wiki/Bovine_somatotropin
2) Feeding animals antibiotics to prevent outbreaks of disease within a herd: https://en.wikipedia.org/wiki/Bovine_somatotropin
3) Packing animals extremely close together (closer than they would be if they were free to wander unimpeded), so that they are exposed to their own waste in high concentrations and over a prolonged duration: https://www.aspca.org/animal-cruelty/farm-animal-welfare/ani... .
A whole lot from one page: https://en.wikipedia.org/wiki/Intensive_animal_farming
4) The major milestone in 20th century poultry production was the discovery of vitamin D, which made it possible to keep chickens in confinement year-round.
5) Meat-type chickens currently grow to market weight in six to seven weeks, whereas only fifty years ago it took three times as long.[Havenstein, G.B., P.R. Ferket, and M.A. Qureshi, 2003a. Growth, livability, and feed conversion of 1957 versus 2001 broilers when fed representative 1957 and 2001 broiler diets. Poult. Sci. 82:1500–1508] This is due to genetic selection and nutritional modifications (but not the use of growth hormones, which are illegal for use in poultry in the US and many other countries).
6) On average, a chicken lays one egg a day, but not on every day of the year. This varies with the breed and time of year. In 1900, average egg production was 83 eggs per hen per year. In 2000, it was well over 300.
7) The use of sow stalls (gestation crates) has resulted in lower production costs, however, this practice has led to more significant animal welfare concerns. Many of the world’s largest producers of pigs (U.S. and Canada) use sow stalls, but some nations (e.g. the UK) and some US States (e.g. Florida and Arizona) have banned them.
8) Piglets often receive range of treatments including castration, tail docking to reduce tail biting, teeth clipped (to reduce injuring their mother's nipples and prevent later tusk growth) and their ears notched to assist identification. Treatments are usually made without pain killers. Weak runts may be slain shortly after birth.
9) Many routine husbandry practices involve ear tagging, dehorning, loading, medical operations, vaccinations and hoof care, as well as training for agricultural shows and preparations. There are also some cultural differences in working with cattle - the cattle husbandry of Fulani men rests on behavioural techniques, whereas in Europe cattle are controlled primarily by physical means like fences.[Lott, Dale F.; Hart, Benjamin L. (October 1979). "Applied ethology in a nomadic cattle culture". Applied Animal Ethology. Elsevier B.V. 5 (4): 309–319. doi:10.1016/0304-3762(79)90102-0.]
10) Farmed fish are kept in concentrations never seen in the wild, e.g. 50,000 fish in a 2-acre (8,100 m2) area,["Fuss over Farming Fish, Alaska Science Forum". Retrieved September 6, 2015.] with each fish occupying less room than the average bathtub. This can cause several forms of pollution. Packed tightly, fish rub against each other and the sides of their cages, damaging their fins and tails and becoming sickened with various diseases and infections.[This also causes stress."Facts about Fish and Fish Farming", Advocates for Animals.]
11) Technological advances have led to growing shrimp at ever higher densities, and broodstock is shipped worldwide. Virtually all farmed shrimp are penaeids (i.e., of the family Penaeidae), and just two species of shrimp—the Penaeus vannamei (Pacific white shrimp) and the Penaeus monodon (giant tiger prawn)—account for roughly 80% of all farmed shrimp. These industrial monocultures are very susceptible to diseases, which have caused several regional wipe-outs of farm shrimp populations. Increasing ecological problems, repeated disease outbreaks, and pressure and criticism from both NGOs and consumer countries led to changes in the industry in the late 1990s and generally stronger regulation by governments.
A few quotes from https://www.theguardian.com/books/2015/sep/25/industrial-far... (I liked this article - you should read it if you have an interest in the topic)
12) Broiler chickens, which are reared specifically for their meat, often suffer lameness due to overcrowding. [https://www.theguardian.com/books/2015/sep/25/industrial-far...]
13)
What happens when farmers now take a young calf, separate her from her mother, put her in a tiny cage, vaccinate her against various diseases, provide her with food and water, and then, when she is old enough, artificially inseminate her with bull sperm? From an objective perspective, this calf no longer needs either maternal bonding or playmates in order to survive and reproduce. All her needs are being taken care of by her human masters. But from a subjective perspective, the calf still feels a strong urge to bond with her mother and to play with other calves. If these urges are not fulfilled, the calf suffers greatly.
This is the basic lesson of evolutionary psychology: a need shaped thousands of generations ago continues to be felt subjectively even if it is no longer necessary for survival and reproduction in the present. Tragically, the agricultural revolution gave humans the power to ensure the survival and reproduction of domesticated animals while ignoring their subjective needs. In consequence, domesticated animals are collectively the most successful animals in the world, and at the same time they are individually the most miserable animals that have ever existed.
14) The scientific study of animals has played a dismal role in this tragedy. The scientific community has used its growing knowledge of animals mainly to manipulate their lives more efficiently in the service of human industry. Yet this same knowledge has demonstrated beyond reasonable doubt that farm animals are sentient beings, with intricate social relations and sophisticated psychological patterns. They may not be as intelligent as us, but they certainly know pain, fear and loneliness. They too can suffer, and they too can be happy.
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