Just two things that occur to me after having arguments about the NHS with people at parties (oh, alright - on blogs. I have no social life; are you happy now?)
1. As long as less than 100% of the economy is dedicated to healthcare, it will always be true to say of any piece of government expenditure that "the money could have been spent on the NHS". This is not an argument against that piece of spending, which might be good or bad but is so independently on its own merits. This is a fallacious application of opportunity cost - although the NHS as a whole is very valuable, it cannot be assumed that the entire budget of the Royal Opera, if rededicated to the NHS, would be used on its most valuable activities.
2. People do things which damage their health. When their health is damaged, they get treated by the NHS, and this costs money, which comes from our taxes. On the other hand, if I really believed that the fact that other people's private activities impose a cost on the NHS gives us a right to interfere in their private pleasures, I would say get rid of the damn thing tomorrow. The NHS was not set up as an instrument of social control and it is downright evil to try to use it as one.
In general, the NHS is a health insurance and health provision system. It works pretty well and it is very popular. But it is not our tribal totem to which things must be sacrificed simply because of its importance and wonderfulness. The cause of having a sensible healthcare policy is not helped at all by trying to use bad healthcare policy arguments to support bad arguments in other areas of politics.