...this seems a lot like if a POTS/VOIP provider announced that instead of charging you the same rate per minute no matter who you called, they were going to start charging you less for some calls, and perhaps even make some phone numbers free to call.
Which now that I write it down like that actually does sound a bit dodgy! (And would sound even more so if you were viewing it from circa-1980, when phone calls were vastly more important, and AT&T has vastly more power and reach than any comparable ISP today.)
Except, of course, we've accepted that sort of price discrimination on phone calls forever, and with 1-800 and 1-900 numbers (or equivalents) we've long been of accepting of very explicit skewing of the costs of phone calls based on business deals worked out between the phone company and the content provider.
So I dunno. I see some arguments in favor of having the providers of networks be strictly neutral when it comes to content. But it also feels to me like this is not a principle we've adopted in other cases, and (for me at least) it's actually quite hard to discern the harm that "harmful zero-rating offerings" are causing.
In fact, I'm not even entirely sure who's meant to be harmed; are we trying to protect consumers or content creators? The article seems to suggest it's other content creators. Which brings up an interesting thought experiment: If zero-rating is fine, would it be okay for AT&T to charge some data at higher rates, and then split the profit with the content creators? :) Eg, "AT&T now offers Netflix as a premium service; all AT&T customers now have a full access to the Netflix service! (Note, higher premium data usage rates apply when viewing premium Netflix content)" Would that be okay? Would it be harmful? To whom would it be harmful? :)
(Note, incidentally, that I live in a country where for many years international data was charged at a higher rate than national data, for fairly obvious reasons involving undersea cables. There's no historical precedent that says all data must be charged the same, even if your personal experience has been that it has been for you.)