The challenge is when all their friends have a phone, and they want one. Sure, if the culture at your kids school is no one has a phone, then no one cares. If not, it's a lot harder, and does have impacts on them socially.
Your kids being the only ones without an tablet/smartphone is social death. Great they are not stuck to a screen, instead they will be a miserable outcast. I agree with your initial post, but the implementation is far from easy and needs an collective approach if you dont want to just ruin your kids lives.
I don't agree that it's social death, because I've seen it managed fine. But I do think that rebellion is inspired from rules, especially over socially popular phenomenon.
It sucks how it is but I've seen plenty of people totally ostracized because they lack internet/social media. Nobody wants to communicate unless it's online.