Gosh I've tried to write this list 3 times now and I've never felt anything was comprehensive enough to put on HN.
So, hopefully the attempt will be sufficient -
<speech boilerplate "want to protect my family, need to keep you informed, if you arent going to get off of the net, then you need to be prepared">
1) Humor is being used to weaponize and radicalize people. A significant group of people who identify as alt right were first introdcued to the ideas via humor. Please be careful of off colour humor. You and me may think it is a joke with no bearing on reality. But there are people who think that its not a joke, and that the ideas behind it
2) Be ware whatsapp - I'm in India and there is a spate of lynchings in rural areas because of whatsapp forwards. People have been killed because they are suspected of being child abductors.
I've personally seen the videos and they are horrific, they include videos of a live child being gutted - but its a gang video from mexico. Another video depicting an abduction, is from a child safety video in Pakistan - theyre spread between maids, drivers, auto-wallahs and office workers.
An Indian state has tried to grapple with this problem by direct communication with the villages, by using drummers, warning people to not trust forwards. Tragically one of the people paid to inform people was himself killed, on suspicion of being a child abductor.
3) Increasing polarizaiton - What started out as mild jokes are expanding into massive cracks in the fabric of my world. A North/South Indian divide has grown from an occasional joke, to an often oozing wound. Online media carries no tone or body language; when people interact in this impoverished environment, our brains end up responding to the strongest emotional versions of a comment. Small fights end up creating lasting grudges.
So don't EVER forward anything mildly polarizing and divisive.
4) Dont trust emotions - almost ANY item which generates an emotional response in you, should be treated as suspect. The best way people have to get you to stop thinking rationally, is by making you think emotionally.
Other things that come to mind are fake news, and the nature of the media formats to keep people on it, and the entire behavioral science behind it. (Skinnerian conditioning, reward schedules, the network effect, responsive design, social approval and so on).
A good point to bring up is depression, and the fact that material on social media is biased, few people talk about an average day or a terrible day or embarrassing things. Humans were not designed to be seduced into believing that the world is great for everyone else and average for me.
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For the normal person listening in good faith, any one of those points is sufficient to create a sense of discomfort.
But ultimately, the main driver is the fact that most people are already uncomfortable with social media and are sitting on a pile of bad experiences.