First of all, I just don't believe people are exchangeable in this
fashion, because of hereditarian considerations; the exchanging of
places before hand would not, in many cases, would not lead to a
significant "shake-up" of society, if meritocracy is truly operating —
so considering things with a veil seems needless.
With respect, I think that this suggests a slight misunderstanding of what Rawls is arguing. He is well aware that people are not created equal. However, what he does believe is that every individual should be taken to have equal moral status i.e. our considerations of justice shouldn't start from the starting point of preferential treatment towards some. (I would imagine - or hope! - that very few would disagree with this as a fundamental part of the definition of 'justice'.)
So, we're trying to work out fair principles that treat everyone as morally equally important, but these principles are to govern over a situation where people are not equal in strength, mental ability, inherited wealth, social connections, and so on. Now, if we actual people were to try to design these principles then it seems likely that, say, on the whole the weakest or poorest might try to design principles that put their interests above all others, whereas the wealthiest and most powerful might try to design principles that maintain their status. The naturally physically strongest might try to design principles that link power to physical aptitude. And so on - and this doesn't seem fair, or workable.
So, how can we avoid this situation? Rawls thinks that we can avoid it by undertaking a thought experiment: if none of us actually knew anything about our social status, strengths/weaknesses, race, gender, etc., but knew that we were about to enter into a society that we were going to have to be happy in, what principles would we choose?
What is actually going on here is that the method, in the thought experiment, of depriving the deliberating parties of information is a way of building in fairness and impartiality into the deliberation. The parties can't possibly be *un*fair to one another in their choice of principles because they wouldn't know how, and wouldn't know whether their choices would actually disadvantage themselves. As such, whatever principles these imaginary parties would choose will be fair and impartial.
Now, we could argue about exactly what principles the parties behind the veil would actually choose, but, at any rate, the above is the method and whatever else we might say one can understand the thinking behind it and appreciate the philosophical elegance. I think it would be a mistake to suggest that it relies on the idea that people could be 'exchanged'; firstly, it is just a thought experiment designed to generate certain kinds of conclusions in the right way, and so doesn't really have a lot to do with actual people, and secondly, its aim is to arrive at principles that can ensure the just social co-existence of people who, indeed, aren't interchangeable.
Secondly, using the veil to argue for distributive justice and
egalitarianism, as Rawls does, in my opinion seems to presume that
moral virtue is orthogonal to societal position, so that it is only
"fair" that we "start off on the same foot"; I don't agree with that
either, because I think the poor, at least in America, are somewhat
less virtuous than middle America or the rich, and that a moral
accounting behind this veil would in any case send these lacking to
the same positions they occupy.
I think I read above that this isn't a forum for opinion so I'll move swiftly on from that one (!...) but I think again Rawls's answer would centre around the idea of the equal moral status of persons (at least at birth). Clearly, many would argue that during life people through their agency makes choices that mean that they 'deserve' or 'don't deserve' certain things, but Rawls thinks that in the eyes of justice every person is still equal; no matter how 'good' or 'bad', people don't earn preferential treatment from justice (we wouldn't say that someone who gives to charity should get away with murder, or that people who are mean to their friends should be stripped of their wealth). Rawls isn't really interested in what people 'deserve' through their deeds (for that you want Robert Nozick) or through some idea of their innate virtue, but rather in having a social system that isn't predestined to militate against the life chances of particular people and groups.
But, alas, I'm a naif in philosophy, having never studied it
seriously. So I have two questions: Are there any prominent attacks on
Rawls' position along these lines, and secondly, if so, have any
liberal philosophers updated Rawls' argument to deal with positions
from hereditariainism and so on?
On your first complaint, that people are different and not exchangeable, there is a well-known critique of Rawls - and perhaps of liberalism and the social contract more generally - that it assumes that all people are essentially equal and the same, when in fact they are not, as is proved by the ubiquitous fact of need and dependence in society. It is unclear that, say, the mentally handicapped or the very old and frail, or young children, can participate in the (hypothetical) social contract that Rawls envisages, and so - the critique goes - Rawls cannot deal with difference and dependence and need. This argument is particularly associated with feminist critics like Martha Nussbaum or Eva Kittay. I've not explained it particularly well but it is easy to look up and is often called the 'dependence critique' of Rawls. Handily for your second question, both Nussbaum and Kittay are still essentially within the liberal tradition and aim to adapt rather than to overhaul Rawlsian liberal egalitarianism.
On your second complaint, that the idea of 'starting off on the same foot' is misguided because virtue tends to increase up the income distribution (at least in the US), it sounds like Robert Nozick would be about the closest to what you have in mind. I doubt that he would express it in terms of the 'virtue' of different social groups, but he too doesn't like the idea of starting off on the same foot because he is interested in property and what it means to hold property justly, and for him as long as property was acquired justly in the first place and has been passed on fairly - such as through a family - then it is still held justly. As a result, his conclusions are essentially very right-wing in advocating almost no redistribution or interference in the market (although not quite as right-wing as suggesting that the poor are less virtuous than the middle class and wealthy and even given the chance would still go sliding back down to a lowly and un-virtuous position...)