Matthew Iglesias cites a paper estimating the impact of union decline on the norm of acceptability of inequality. This is fascinating stuff, and picks up on a point made tentatively by Krugman a while back - market forces, globalization, welfare retrenchment and so on are not the only reasons for growing inequality. It matters that inequality has become more socially acceptable, and the role of unions is sustaining norms of 'fair shares' in the past was important. Time to grow the unions again!
Interestingly, today Ed Miliband launched a consultation exercise to investigate how the 'squeezed middle' could be defended from falling living standards. The Guardian headlined it by pointing out that the superrich have gained a large chunk of income gains over the past 25 years. No-one mentioned the decline of unions in this process, and my guess is Miliband will avoid the subject like the plague. Electorally he may be right, but it's hard to imagine an egalitarian society without unions that are a lot stronger than in the UK.