I would not disagree :) and i think they came up with unlimited data plans just to label bytes in the future. And they are already doing that. You can already buy a plan with 10gb Facebook + 10gb whatever you want. Makes me sad.
There is only one justified reason for phone companies to check if you are using your phone as a router, and that is when they provide unlimited data to your contract. Unlimited data is provided given that you are going to use it on your personal devices and not to act as an ISP to everyone around you. Other than that you generally pay for X GB of data and it is none of their business how you spend it.