The move away from Defined Benefit Pensions was one of necessity, they just aren't maintainable and never have been.

First off it is important to remember that Defined Benefit pension do not have a very long history in the private sector.  The first might have appeared in the 1920's or 1930's, but they really weren't very common until the mid to late 1960's and started falling out of favour in the mid 1980's.  Since the recession of the early 1990's you'll be hard pressed to find newly created Define Benefit pension plans in the private sector.

So we're really talking about only about a 20 to maybe 30-year "golden age" of Define Benefit pension plans. 

The reality is that DB pension plans just proved to be unsustainable.  When a recession would hit a company would see revenue plummet at the same time that a DB pension plan required increased contributions.  Revenue declines and cost increases lead to only one thing: bankruptcies, which help no one, least of all plan members.