Firstly, I do not believe that the interests of 'the state' and the interests of 'the people' are identical. This is because I rather doubt that there is any such thing as the interests of the people. The idea of the general, or popular, will can be traced back to Rousseau. As generally interpreted, Rousseau suggests that there is such a thing as the General Will, which is not to be identified with the particular will of any one group of people within a society, but with the collective will of the society as a whole. How this will is to be discerned is a matter of some difficulty. (Rousseau's own view seems not dissimilar to liberalism of the type espoused by Rawls). However, the more problematic issue with Rousseau is that he thinks that people can be forced to follow the general will, and that this equates to forcing them to be free. This idea that one can be made more free by the state's coercive activity is pretty disturbing, but follows logically from the belief that the general will really is the will of society as a whole - that which it wills for the good of all - and therefore it is at some level also your particular will as a member of society even if you do not know that. You are only being forced to be true to yourself. Or some such nonsense.
There are two issues with this. On the one hand, there is no general will, no will of the people - only the different desires and aspirations of different groups within society, such that at its best the state could only represent the interests of some and not all of its people; on the other hand, the state itself is not a cypher, but is made up of particular people who have their own desires and aspirations, such that the state is likely to represent primarily the interests of its own stakeholders and not society more broadly. It should be clear that the larger the state is - the more the state does - the less likely it is to be working for the common good; broad guidelines could be in everyone's interests, but detailed legislation is much more likely to favour one group over another. This is why traditionally the state has been seen by many political theorists as at least potentially the deadly enemy of the people, and not their friend.
Secondly, I think that even when the state seeks to be benevolent, what it ends up doing is exercising ever-tightening control over people in society. Consider this: if the state taxes heavily in order to finance universal health care, then there is suddenly an apparently good argument for the state to control your behaviour in order to make you healthier. If the state generously offers free universal education, the state gains control over how and what your children are taught. I deliberately pick two examples of state provision of which I strongly approve to illustrate how dangerous the creep in growing state power can be, and also to show that I am not against state provision of services per se. I simply think that they come with a serious health warning.
How does this map on to my theological beliefs? That deserves a post in itself, but to summarise:
1. I don't believe the state is a redemptive organ - it belongs in the sphere of providence, not the covenant. This doesn't mean it can't do good, but it does mean it can't do ultimate good.
2. I don't believe that the state is in view when Christians are instructed to care for people; I think it is a tragedy that the Church has generally handed this role over to a new provider.
3. I do believe in the redemption of societal structures; but I believe that we must wait for the return of Christ to see it.