Bias against liberty / Immigration - no comments

Chris at Stumbling and Mumbling reminds us of the salience heuristic (more here on the Wikipedia) in attacking Rod Liddle's theory that tighter immigration controls might have prevented al-Qa’eda from organising within the NHS.

Specifically, the criticism is of the idea that the imagined policy of tighter controls would have been implemented 100% successfully, so that we would never be able to look back in hindsight and spot a dangerous individual who had slipped through the net (a false negative), while the 'right sort of people' would continue to be allowed through without (a false positive) hindrance or persecution.

Perhaps one way of looking at this kind of policy in practice is that each application of immigration policy - let's say, the processing of a particular case - must feature a particular probability of error: a probability that might increase with political pressure, with an increase in staffing levels and consequent average decline in competence, and might decrease with greater resources per head. A tighter policy - more application of policy - must, all else being equal, lead to a greater number of errors, whether that be terrorists being allowed in, or 'genuine'/'valuable' people being denied entrance/sent packing. The assumption that all the new resources can - rather than being spread around the system, making more mistakes of their own, throughout - be directed by an omniscient force to solve the existing errors, is illogical as well as hopelessly far-fetched.

Assuming both types of error make us equally unhappy (don't they? If not, please elaborate), surely only improved detection offers us a way of reducing errors - that is to say, differentiating potential terrorists from valued future citizens. Let any additional resources/legislation be directed there.

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The original purpose of this post was in fact to link to the Friedrich Hayek quotation that Chris cites (my emphasis):

Since the value of freedom rests on the opportunities it provides for unforeseeable and unpredictable actions, we will rarely know what we lose through a particular restriction of freedom. Any such restriction, any coercion other than the enforcement of general rules, will aim at the achievement of some foreseeable particular result, but what is prevented by it will usually not be known... And so, when we decide each issue solely on what appear to be its individual merits, we always over-estimate the advantages of central direction. (Law Legislation and Liberty Vol I, p56-57.)

Beat that.