Alan Milburn's latest report on social mobility says (pdf):

The senior ranks of the professions are a closed shop. If social mobility is to become anything other than a pipedream they will have to open up. Unfortunately, the evidence collected for this report suggests that there is only, at best, limited progress being made in prising open the professions. That is not about to change any time soon.

This raises a question: why is he so keen to increase social mobility?

I ask because it's not obvious that social mobility is wholly desirable. Certainly, it's not sufficient for an acceptable social structure: Imperial China and, I suspect, the Soviet Union had some social mobility, but few applaud such societies.

And at least three political perspectives are sceptical of it. To libertarians, employers (in the private sector) have a right to employ whomever they wish regardless of talent - and the public sector and BBC seem to have embraced this principle. To Marxists, an opportunity to become an exploiter does not legitimize exploitation. And to liberal egalitarians, talent is morally arbitrary so it cannot easily entitle one to a "top job". Yes, Rawls wanted fair equality of opportunity, but he yoked this principle to the idea that inequalities be permissible only to the extent that they improve the lot of the worst-off.

Nor is it obvious that social mobility is desirable in utilitarian terms. Greater social mobility would create isolation amongst people from poor backgrounds who "made it" (trust me, I know), and self-recrimination among those who didn't.

Several thinkers, from Michael Young to Matt Cavanagh, have for these reasons opposed equality of opportunity.

Nor even is it obvious that social mobility is necessary for economic efficiency. If there's a correlation between the poshness of doctors and iatrogenetic effects, Mr Milburn does not provide evidence for it. And I'd suggest that, in banking, social mobility has had catastrophic effects; banks prospered for years when they were run by the old boy network, and collapsed soon after meritocratic physics PhDs and sons of electricians took over.

So, what use is greater social mobility? The answer, I fear, is that it can act to legitimate inequality. As Brian Barry said, a belief in equality of opportunity "cloaks the status quo with legitimacy through a process of mystification."

This works in two ways. One is that the perception that there are opprtunities to get rich reduces people's desire for redistributive taxation.

The other was pointed out by Michael Young:

If meritocrats believe, as more and more of them are encouraged to, that their advancement comes from their own merits, they can feel they deserve whatever they can get.
They can be insufferably smug, much more so than the people who knew they had achieved advancement not on their own merit but because they were, as somebody's son or daughter, the beneficiaries of nepotism. The newcomers can actually believe they have morality on their side.
So assured have the elite become that there is almost no block on the rewards they arrogate to themselves.

In these senses, the desire for more social mobility serves not egalitarian ends, but their exact opposite.