Sorry, but I have to politely disagree with most of the comments above.

If seats would be permanently locked in an upright position, that would also mean that you would not be able to 'stretch' out in case a flight would not be so fully booked. Overnight/redeye flights frequently have a lower load factor, and I would hate to have to sit up straight on one of those across the country...

I suggest that instead airlines focus on increasing leg room a bit....