Firstly there is no public responsibility for ensuring that Three is profitable. It isn't even a UK firm, being owned by Hutchison 3G of Hong Kong. The Three group has lost billions of dollars on speculative 3G networks and trying to find room in the UK between Vodafone, 02, T-Mobile and Orange has been a largely futile task. If the other four major networks also have to cut their termination caps then Three should be treated no differently. It isn't the fault of the other companies that Three hasn't got enough customers and that more people phone out of Three's network than phone in to it.
It is also total crap that the problem Three has is the supposedly "broken" regime the UK has in moving your number from one company to another. The problem Three has is it just doesn't provide an engaging enough reason to move to them in the first place, they're expensive, riddled with gimmicks, expensive and their tariff is confusing. If Three didn't exist, no one would invent them.