Why should pensioners not face counter party risk like the rest of us?
Pensioners in the private sector do face those risks.
The whole point of a pension is to accept lower pay today to not have to worry about tomorrow. It's a structural way of dealing with the fact that most people don't know how to plan for the future and, before, just ended up dying in the streets in their 60s.
That doesn't answer the question of why they shouldn't face counter party risk like everyone else though. Obviously, the government also doesn't know how to plan for the future.
What's wrong with dying in the streets in their 60s? They're better off than the 99% of humanity that lived before them. Why should the next generation pull the weight of the previous?