There's a big difference between "the state should start doing something that it does not do/hasn't ever done" and "the state controls something and it should change the way it does that".
That's not pedantry. That's the difference between "darn gub'mint won't let me land my private jet on the freeway" and "darn gub'mint lowered the speed limit on the freeway".
If you want to argue that the state shouldn't control phone use related to social media, you need to engage with the ways they already control phone use, and whether/how well those work (and have a complex conversation about the costs/benefits of adding an additional control); it's dishonest to frame it as a qualitative shift from not restricting what adults do on their phones to doing that.
No it's pure unbridled pedantry. The state does not allow you to use any object or thing to break the law, including your own body. Thus by your definition the state "controls" everything, making the distinction irrelevant.
Imagine making this same argument but for something like slavery: "Well, the government already controls what we can do with our bodies, so the concept of forcing some people to a life of hard labor will require you to engage with the ways they already control peoples bodies, how well they work, and we should have a complex conversation about the cost/benefits of this additional control. It's dishonest to frame it as a qualitative shift, it's more akin to the government lowering the speed limit."
We can also just say no. End of discussion. You nor anyone else gets to tell me what otherwise-non-illegal media I can consume.