I think the question that really should be asked is what do we need to protect young people from?, because I don't think we should prevent children and teenagers from socializing through digital platforms, or being able to access all the valuable content available on such platforms.

Addiction and doom-scrolling

A lot of "social media" uses psychological techniques to create an addictive experience. Having such a dependency and consuming any one thing excessively is clearly harmful. So it would make sense to have an age limit -- similar to alcohol or gambling, you need to be of a certain age in order to even have the ability to resist and manage such things responsibly.

It would be these dark patterns of user experience design that it would make sense to put an age limit on -- not "social media" (a lot of games for instance also try to make you addicted and make you keep playing long after you stopped enjoying it).

However, neither the social aspect nor the valuable content on these platforms actually needs it to be addictive and harmful - unlike things like alcohol and gambling which are to some degree explicitly desired for their inherent vices. These practices, which no consumer ever wants, could actually be make completely illegal and we'd still retain all the good stuff.

Advertisement and manipulation

The power of manipulation that various forms of advertisements have should not be underestimated. The entire point of marketing is to get you to do something which you otherwise would not have done. After all, if you'd done it without seeing the ad then showing you the ad would be a complete waste of money.

Limiting how much people are exposed to marketing campaigns would be a good thing, especially for young people who are not mentally equipped to critically examine the advertisement while keeping in mind that they are directly being influenced for someone else's gain. A lot of adults aren't particularly good at it either, though.

Again, this isn't about "social media" but about one aspect that they commonly include, but is also found in a lot of other places. It makes more sense to age limit and regulate this aspect rather than "social media", and in fact most places do have laws about this already, but they probably need some updates that take modern developments into account.

Fake news and misinformation

On most "social media" platforms, the creators don't care much about whether the content is truthful or not. Part of this is because they don't really care much about their users at all -- they care about their advertisers! They're running a business, and when you do you care about are those who're actually giving you money. Who pays for "social media"? The advertisers.

The other part is that people find fake news to be much more interesting than the truth, which leads to more time on the site and greater engagement -- and so does fear mongering and polarization too, as well as many other ways of misrepresenting reality.

This isn't news -- just look at the news. Every single article is exaggerated and heavily biased to present a certain narrative, and comes with an especially clickbaity headline and image. What's new is that now the entire platform is conspiring against you, using sophisticated algorithms, a multitude of data and artificially generated content to manipulate each and every user individually on a personal level.

Unfortunately, in this case laws won't help much, partially because defining misinformation is highly subjective, and partially because these platforms do need to make money in some way or they won't exist. If the users would pay for "social media" then they would be the customer and their needs would become the primary focus, and the need to be valuable enough to pay for arises.

Additionally, in a subscription model (rather than "pay-per-view") maintaining value over a longer term is prioritized and the grater stability of the customer base reduces the need for sensationalism. This can be seen in the history of physical news papers as well.

Bad content and censorship

One reason common reasoning for age limits is that young people need to be protected from certain types of content that might be considered bad for them; like sex and drugs. Personally, I believe education to be a much better protector than censorship -- especially since young people will sooner or later have to grow up and live their own lives. Will they then have the tools to deal with it, or will they be unequipped and unprepared?

That parents want greater control over their children's access to "bad content" is however understandable, and can be an important part of introducing it at an appropriate age and for parents to explain it in the right context. What "bad content" is, and when it becomes age appropriate is of extremely subjective and having the government enact some kind of blanket censorship because some people are upset and have poor relationships with their children is a terrible idea.

Luckily, we already mentioned a solution. Having to pay for access to "social media" directly involves parents in the kinds of platforms their children use. This creates an incentive for platforms to moderate their content and uphold reasonable standard, and even provide parental controls, or else the children won't be able to convince their parents to pay for it.

It's simple economics, all businesses work to satisfy their customers. If you want "social media" to work for your and your children's interests -- you need to pay for it.