Your attitude seems to be "I should be able to get a cheap phone from a carrier by agreeing not to tether, and then I should be able to violate that agreement anyway, and this is a totally moral position". Phones are a commodity. You can get them anywhere. Want to tether? Buy a phone and a plan that allows it. Problem solved.
Which is why it baffles me beyond all limits just why so many smart Americans go out of their way to defend corporate practices that hurt them as customers.
Why are you trying so hard to support your telcos decision to make your life worse?
If everybody in your neighbourhood turned their faucets on at once, water supply would simply stop working. So?
This really isn't complicated. If your carrier contract doesn't forbid tethering but they sold you a phone that does, take it up with them, that sounds messed up and rare. If your contract forbids tethering then you're just trying to weasel your way out of a market you voluntarily entered in to. That's the opposite of the free market.