No-one thinks the NHS is perfect. People are rationally defensive of it because the most likely alternative is not something like the German system (which is better, but has major problems) but a sale of the NHS to an American company such as Kaiser Permanente. Most people are well aware of the deeply rooted problems of the American system, and recognise that almost anything is better than that. Any systematic change would require a government which is trusted to handle it. That rules out the Conservatives (who are in power most of the time) as even their supporters don't trust them on this issue, and Labour is unlikely to either have the inclination to implement deep changes, or be in office long enough to effect them.