Why are so many prime-age men not working?

Scariest statistic of the Great Recession: nearly 20 percent of all men aged 25 to 54 are not working, according to recent NYT pieces by David Leonhardt and David Brooks.  To give you some perspective, 96 percent were working in 1954.  A small part of this reflects the growth of graduate education and earlier retirement.  A big chunk is growth in the disability rolls; ten years ago we had 5 million Americans on disability, now we have 8.2 million. It is hard to imagine that jobs have become that much more dangerous or health conditions have declined so much over the last ten years, so economic incentives must be driving most of this growth.  Research shows that once a person starts to receive federal disability payments, the odds of working again are near zero.  This is an economic and social issue that likely will receive more attention.