Of course the possible return rates are estimates. Sales forecasts, profit forecasts, etc. are done in most businesses all the time. All of them are estimates. That doesn’t make them wrong.
Because the government or the tax payers have a stake in GM, does that mean GM shouldn’t make any business decisions that cost money? They shouldn’t advertise, offer incentive programs, or implement any other program to sell cars and improve their business? What about warranties? Shouldn’t they eliminate those? Aren’t they being paid with tax payer dollars? Perhaps they shouldn’t introduce any new models. After all, wouldn’t they be gambling with tax payer dollars that those new models will be successful and profitable?
The bottom line is if GM is going to become profitable again, it has to run like a business. It has to take the calculated risks necessary to be successful in business.