Controversial but honest question: How do anti-ads people propose the free open internet monetizes itself?
Volunteer basis or charge users. Optional subscriptions keep small webforums alive, like HN would probably be fine with some kind of 10/mo thing. Maybe charge a small fee for new accounts? For things that need to scale past that like very large social media, the question is if that's worth those sites existing.
This notion is a very Silicon Valley / coastal elite mentality IMO. A significant majority of people on the internet do not and will not pay for anything - largely because most people around the world just don't have the money for stuff like that.
The data on this is pretty consistent - take Netflix for example. A majority of Netflix users choose the cheaper ad supported tier, even though it is very easy and only marginally more expensive to switch to the non-ad supported tier. And this is already filtering to the subset of people who are willing and able to pay for a streaming subscription to begin with. The same case exists for Reddit -> you can pay to have ads removed, but only 1% of users do.
I see what you mean by Hacker News, but it's not a great example, since there are currently no ads and it's free. It's provided by Y Combinator, which monetizes via investing in startups (not something all internet businesses can reliably just start doing). For example - how would Reddit monetize? You cannot really expect people on Reddit all to be willing to pay to use it. And if some were - the whole value of a network is its scale -> so the drop in users would effectively kill the site. That's why there are no subscription only forums out there (at least none that I know of).
With regards to your second point of if these social media sites should even exist in the first place -> that's where you the consumer get to decide. If you don't get value from it, just don't use it. People who do get value from it -> use it. If enough people collectively decide it's not valuable, then the website becomes irrelevant (see Google+ and MySpace).
This is where I get very confused by anti ads people - show me a reliable alternative that is proven to work. Show me that people across the world, not just in San Francisco or London, can and will pay to access these websites/apps. And I'm not just talking about Meta - what about every random small website you have ever accessed that is ad supported? What about news websites like BBC? Or independent content creators who monetize via Instagram / YouTube ads? What about that wiki for that favorite video game of yours? Or that cooking blog? Don't get me wrong - I hate seeing ads as much as the next guy - but I can't really picture a realistic alternative.