TLDR: As a high school level teacher, this would be less of a problem if teachers had stronger enforcement powers. Since we often don't - I would strongly favor a ban. If students need a computer, we have them available all day, every day.
As a high school level teacher, I appreciate the attitude that there are amazing opportunities for learning and skill development with computers. I agree with this wholeheartedly. That said, a majority of my students are addicted to social media (they are teenagers, after all) and cannot self moderate their attention and/or behavior on this issue. They are not, generally, breaking their attention away from class for some other kind of educational outlet (for which I am already fairly lenient when appropriate). They are sending their friends snaps, plays both games, and texting.
Of course, using phones in class is already against school policy, but it will remain and issue until I am able to take a phone away from a student. At a prior school, this was explicitly against policy becuase it was considered a liability issue as phones are expensive personal property that the school
did not want to be responsible for them. Additionally, parents give minimal support and/or flip out when it happens. Very few have the willingness to keep their student's phone at home during the school day even when it is a known and acknowledged problem. Often, they simply don't want to argue with their teen about it.
I believe that we - as a American culture - are still too enamoured with our smart phones to effectively acknowledge the potential negative effects they can have on our attention/learning/cognitive development.