I wonder what results you'd get if you separately polled, say, under-25s and over-25s on whether the increasing use of smartphones in public is a bad thing.
I also wonder if complaints about "people have their heads in books all the time, they don't talk to each other!" were a common thing when novels began to be broadly popular in the 18th century.
The cause of concern is what appears to be lack of moderation combined with disregard for others. Using smartphones in public? Fine. Using smartphones in public such that you bump into other people/things and disrupt others? Not cool. You can replace 'using smartphones' with 'reading' and it works the same way.
I also wonder if complaints about "people have their heads in books all the time, they don't talk to each other!" were a common thing when novels began to be broadly popular in the 18th century.