There's a lot of "we've always done like that" in those arguments.
A good chunk of those domains (friendship, dating, academics, politics, family dynamics, identity, for instance for sure) can exist over the internet as well. To quote a wise man, "we say AFK, not IRL, because the internet is real life, too". And it's going to be even more so in their adulthood.
We have no idea what the world is going to look like in 30 years. What if the skills and mindset they learn by looking at their smartphone all day end up being more important than the in-person social skills this guy wants to replace them with?
The nerds of the 80's that parent encouraged to turn away from computers have now become highly paid software engineers. What if you're crippling your kids' lives and careers because you want them to grow up the good old, traditional way?