That's exactly my point, but we're getting a nice deal right now.
Right now at&t charges the 2 GB people as if they were 1 GB people. They can do this because the vast majority of them are actually using less than 1 GB. So that works out fine for them.
So we're getting 2 GB for the price of 1. Great.
If we were to go to an actual "pay per GB for reals" plan, I'm certain the $25 plan would suddenly be 1 GB and 2 GB would cost more than that. As higher-data users, most of us here enjoy the fact that we use the upper limits of our plans...upper limits that are mostly just silly marketing-speak for the regular public that will never use them. We're getting a deal because they think '2 GB' sound better in their ads, so they say it knowing that most folks will never use it. Lucky us.
Making tethering free is not the problem in and of itself. It's that it would force at&t into charing us for exactly what we use. I don't believe we're paying that right now.