It's part of us being social creatures. Why do we have conversations? Why do we socialise? Why do we do anything that isn't stritcly essential? Because that's how most humans are. There's pleasure to be had in sharing, seeing others, exchanging information, and just human contact. There's plenty of negative possibilities too of course, but that's life, and they can be mitigated against in various ways (as others have said above, using watermarks to reduce copyright infringements, controlling who sees what with filters, etc).
More specifically in my case, though I share much less than I used to (mainly because I take far fewer photos), I have seen that others respond in positive ways when I post stuff, and I enjoy seeing others' output, so it's for the benefit of us both. I've also learned a huge amount - a lot of my online contacts are botanists, bird watchers, and others involved in nature recording and education, and I've found that the constant trickle of images of plants, animals, weaher phenomena, etc. is an excellent way to learn identification skills, and sharing one's own pics is a part of that. Finally, it's a great way of experiencing the world if you haven't the means or the time to go to all the places and see all the things for yourself. We live in a golden age of recording - but without sharing, next to nobody sees most of it.
Funny, our camera club had a big brainstorming meeting about increasing membership. There was a consensus: People now have other places to share their images so camera clubs aren't as important.
I'm not so sure about this specific reasoning, but I do believe that smartphone use has eroded socializing in all areas. Or maybe it's the Web generally? All I know is that much more than brick & mortar shopping is being affected. Clubs of all kinds. Churches. Sports leagues, including bowling and softball. Eating in restaurants. Strolling through malls, strolling down walking streets (though here in the USA, mentally ill, drug addicted homeless panhandlers contribute to the deaths of downtowns--not because of their own intentions, but because of my country's refusal to deal with mental health as a social problem)...
Street photography is more challenging because of social media. People, to me, seem paranoid now when they see a big camera. (Ignoring smartphones!) They are concerned they will be on somebody's blog or Instagram or facebook page, that their privacy is threatened. And heaven forbid a child is in the frame! Almost as bad, so many pedestrians are looking at their smartphones that pictures of spontaneous, interesting subjects are fewer and fewer. Still there for the patient, the diligent, the brave, but not like just a few years ago.
We are enjoying an era of splendid isolation.
So we share selfies and meticulously processed "art" on social media. Some of us are lucky enough to have prints in galleries, but mostly our work is greeted by silence. With a thumbs-up.
In the five years since the this thread was last active, I'd say social media is _______________________ (FILL IN THE BLANK)
TBH, I don't directly. I link from my personal site, just like here and everywhere else. Some people enjoy being 'friends' with everyone which is comedy in itself but many people I work and spend time actually talking with do not have a FB account, an IG account, an <insert social network> account. Its fun to have conversations with friends and new people about something that isn't already a dead horse and that is hard to do if you shared all the details on 42 platforms.
Social media isn't terrible but after watching the hordes trample formerly pristine areas to get their selfies so they, too, could have their moment of 'fame'...
When I post most photos of people, its to one of several a restricted membership groups. Of course, I post photos to illustrate points I'm making during posts like a photo of a piece of equipment or a broken item. I may post photos of funny things like the turkeys on my bird feeder, or of wild animals in my yard, things that Facebook friends might want to see. I also sometimes post photos of food I've prepared, again to illustrate a point.
Most of the really good photos appear in private groups.
Facebook: To share with family, friends, and potential customers (4 paid jobs so far, and I get my rate... I am an amateur that charges at the high end for a portrait session. $350 for 2 hours + expenses). I don't watermark anything and most all I do is TFP. Any money I do get goes right back into buying gear. What's somebody going to do with a stolen low resolution photo? Watermarks can be removed anyway. I only post photos I have asked permission to post first... including those of my grandson from his mother.
Flickr? Because it is fun to post high resolution. Again, I don't watermark anything and the copyright is in the exif.
Instagram: I have a lot of trouble posting to Instagram.
I have some learning/cognitive disabilities that make it very difficult for me to learn all these platforms and how to use them. Any photos I process for anything are very minimally processed. I have to get it right in camera and mostly just adjust exposure a little and resize. That's about all I know how to do. I've really tried to learn, I just can't retain the information unless I do the same thing dozens and dozens of times. Frustrating as heck. It didn't always used to be that way.