Because people use it to vent
One of the most important uses of Facebook is venting. When something bad happens to someone, he uses Facebook to express his concerns. This action helps the person feel better, but it spreads negativity.
Positive people write negative stuff
Some people mistakenly think that by removing negative people, their Facebook newsfeed will contain positive posts. There are usually no negative or positive people, but instead a positive person can write a negative post if he has been through a bad day.
Because some posts are tempting
Some posts, especially the ones that express strong views, can be very tempting. Those kinds of posts usually leads to negative comments and unpleasant debates.
Irrelevant is annoying
Irrelevant posts are annoying. When a person sees a very irrelevant post, he will usually feel annoyed even if it isn’t bad or negative.
Comparisons result in misfortune
If a person is studying hard at home then sees others having fun on the beach in a Facebook post, there is a very big chance that this person will feel really bad. While the post isn’t negative, it causes a lot of negative emotions.
Mixed messages result in unpleasant emotions. A person could see a positive post, then a negative one, then a tempting one about politics, then an irrelevant one. The combination of so many unrelated messages makes Facebook very negative. (See 17 Reasons Why Some People Prefer Twitter over Facebook)
Each day a person checks Facebook he usually has high hopes, but when he discovers that the notifications came from unwanted people he feels bad and disappointed.
Negativity is contagious
When a person gets exposed to so many negative messages, most probably his mood will change to the negative too. Because negativity is contagious, Facebook users keep infecting each other with negativity.
Comparing social status
All people unconsciously compare the number of likes and comments they get to their friends’. People who care too much about those factors are very likely to experience negative emotions because of believing that they are not as popular or loved as they should be.
Remembering the wrong people
Because the newsfeed is so random, a person can come across someone he barely likes or a person who caused him pain. By just remembering those people, a person can feel bad right away.
After spending some time on Facebook without coming out with any additional social benefits, some people feel guilty for wasting their time or ruining their mood for nothing.
News is usually negative
Facebook is a place where news is posted as soon as it happens. Because the news is usually negative, those who check Facebook and come across recent news might feel bad. (See Study Summary: Facebook makes you unhappy and jealous)
How to Open the Desktop version of Facebook on Mobile Phone? View Full Desktop Version of Facebook on Android