That makes no sense, it’s essentially the same as saying the almost 80% of iPhone users that buy it on contract shouldn’t be buying it at all.
It's all unsecured consumer debt. How frequently would the average person upgrade if they had to pay cash out-of-pocket for a new phone? How many phones would Apple (or Samsung, LG, etc.) sell if no financing was available for phones? How much would an iPhone cost if financing wasn't built in to the price?
Like anything else (homes, cars, education, etc.), the 'price' of phones will continue to increase as long as financing is available to maintain demand.