If you live in England, a leaflet entitled "Better Information Means Better Care" should land on your doormat some time this month.

It's from the NHS and announces changes to the way that health officials will handle confidential medical records. Health policy nerds may also know it as "care.data".

From the spring, medical information about you that was previously only kept to help understand you as an individual – information from consultations, notes on prescriptions – will be uploaded to a central database to become one of the world's most complete health databases. Our records are being connected to make them stronger.

This is, in many ways, awesome. Many medical researchers are excited at the prospect of all this data (eg work on superbugs like MRSA). And they should be. Analysis of NHS patient records first revealed the dangers of thalidomide and helped track the impact of the smoking ban. There's so much more it can do under care.data. This new era of socialised big NHS data could be very powerful indeed. I like the idea that my medical treatment will, in the future, be more robustly based on such a large evidence base. I like giving parts of myself to society because I get way more back out of it in return.

But there are reasons to be sceptical. Here are three.

Firstly, this knowledge doesn't just have a social good, or multiple individual health ones. It has economic value too. Indeed, a cynic might argue that the reason the government is pressing this policy through now is precisely because such data will offer financial benefits, and that any to wellbeing are simply pleasant side-effects. (The same cynic might argue that there are parallels with the government policy on open access. I would have some sympathy with that cynic.) It's about boosting the UK life sciences industry, not patient care. This is science policy – where science lies under the auspices of the Department for Business, Innovation and Skills – not just health policy.

I mean, why are we socialising health data at a time when we are also breaking up the core of a socialised healthcare system? Isn't that a bit weird?

As the Guardian science correspondent Ian Sample put it, the project "redefines what it means to be an NHS patient". But is it redefining us because it asks us to give some of our information, or because it is turning yet another part of us into a financial asset? This is an invitation to have a new social contract with respects to our health, one that is very different from the sort of social contract we were offered with the emergence of the NHS.

Secondly, it is worth asking whether we are comfortable giving this sort of personal information out to a collective pot, because it is different from paying taxes. Privacy organisations are understandably concerned.

The Wellcome Trust undertook some interesting public attitudes research on the topic last year. In some respects, the results aren't surprising in that it suggests their concerns over sharing health data comes down to questions of trust in institutions. What was striking, however, was that the people the researchers talked to felt their trust in major institutions was particularly low: with the banking crisis, MPs' expenses, phone hacking, police spies and so on. The researchers found significant fear of being a victim of fraud, with a lot of cynicism towards the government, corporations and press. The research was conducted before the NSA scandal broke, which in some ways dates it, but also means the results aren't tainted by the dominance of that story.

Although a couple of anecdotal data breaches within the NHS were mentioned, faith in the NHS itself seemed reasonably strong. However, there was some uncertainty and concern expressed about the future ownership of health services. People might trust the NHS with their data now, but were scared about what might happen in the future. There were concerns that, as more of the NHS is sold off, personal health data might get into the "wrong hands" outside the NHS, and should be heavily protected from employers, advertisers, insurance providers and even drug manufacturers. Concerns were also expressed that with more funding cuts, the NHS might cut corners, or be more likely to use data against patients to withhold treatment (eg you once smoked, we won't ever give you cancer treatment).

Most interesting perhaps were the differences between the people interviewed, especially class. Basically, the poorer research subjects felt less powerful when it came to dealing with any problems that might occur; arguing their case on identity theft, for example, or fighting unfair use of data by employers. Because that's what happens when you cut and sell off social systems like the NHS or legal aid. Society stops functioning as well as it did. And then you can reap the various benefits of that society; be they economic or something more ambitious.

Thirdly, we should be asking why this policy is being pushed through with so little debate. As the leaflet and website say, you have the choice to opt out. It is there in bold in the cover. But go looking for how to opt out, and it's harder to find. You have to contact your local doctor. It's not simple. The government knows most won't bother. It's also worth noting that the Wellcome research found several gaps in public understanding of the issue. It may well be a good idea, but if we're not ready for it, is it really fair to implement it?

As a strong editorial in Nature last week put it, this whole process is a public-relations exercise that is far too reassuring. It glosses over data security "overly reassuring the population that its personal data are safe is an invitation to public disillusionment in the system down the road" in ways that may easily backfire. It would, I think, be awful if we lost public trust in the idea of NHS data sharing because we end up losing trust in the way this particular policy has been built and the institutional context around it (really, have they learned nothing from BSE, GM et al?).

Should you go through the bother to opt out? It's up to you. I suspect the time would be better spent fighting other "reforms" to the NHS, as well as those to education and legal aid. But there are huge reasons to be angry about this policy, and I think it says a lot about the government's approach to science, healthcare and the wellbeing of the people.