Email is insecure and was overwhelmed by spam, driving people to use systems (such as Gmail) that are good at filtering spam.
Any distributed system will need to figure out how to deal with spam and abuse. That's hard to do without there being a dedicated team to deal with flagged messages.
It's hard to deal with spam and abuse even when there is such a team or effort. That's one reason Twitter is struggling, because unlike Facebook (where people can at least be semi sure only friends/family/connections view their content) Twitter is open to the public to view anyone's profile that isn't explicitly private.
Moderation ends up becoming an awkward balancing act between not completely restricting freedom of speech and stopping trolls/bullies flaming the hell out of anyone they disagree with while simultaneous trying to make it scale. Which is perhaps even harder than determining between what's free speech and what's a threat/harassment.
If someone can come up with a social network that doesn't discriminate between people from different backgrounds/with different political stances while filtering out actual trolls and which manages to do this on a large scale without a huge team of human moderators, then they'll likely pose a massive threat to the existing sites in the market.
It's very true, but this is a known and heavily researched problem. We have solutions to it, compromised solutions perhaps, but solutions none the less.
The current state of social networks vs email is night and day. I would never host my own email (despite self-hosting almost all my other online services) because the anti-spam techniques in wide usage are so punitive if you get your config wrong (your IP and domain basically get permanently sin-binned), but I use gandi.net as my email provider, I'm able to choose to pay them money and in exchange get my mail handled by someone I trust.
I'd gladly pay to use facebook, but run by someone I trust. However, social services are centralized to such an extreme even vs email that I actually cannot pay to have secure and respectful social networking, as facebook has successfully locked everyone else out of the game.
I digress. Email is not perfect, but it's a hell of a lot better than social.
Then you miss out on the social discovery aspect which is a key part of social networking. You're just avoiding the problem of where to go by cutting off your own legs.
Seems contextual whether that's good or bad: one theory of sleep is that we lose consciousness so that we don't go out and get ourselves killed in low visibility conditions.
Social discovery is obviously something people want or they wouldn't use social media services in the first place. Pointing to the existence of other contexts where that doesn't matter is neither relevant nor insightful.
It's like saying 'why worry about these problems, just don't don't use the the internet at all.' I still like paper books and other things and usually spend a day a week off the internet but that doesn't help anyone who's trying to solve an internet problem, does it?
Any distributed system will need to figure out how to deal with spam and abuse. That's hard to do without there being a dedicated team to deal with flagged messages.