I started working at 16. When I was 18 I took two weeks off to go on holiday before I started a new, full time, job.
After a few weeks I was summoned to an appointment at the DHS (as if was then) office where a middle-aged man thrust his big red face into mine and yelled at me that I had NI contributions (2 weeks) missing and that my State Pension depended on full contributions and I would suffer an old age of penury. I must make them up immediately.
That sounds to me pretty much like a contract: I pay the contributions, the state pays my pension when I retire, regardless of my situation. If NI is for other things than providing the payer's State Pension, then that should be made absolutely clear. I have never been told that officially.
If I had paid 12% of my salary into a private pension or a saving scheme from the age of 18, I would probably have ended up having enough to fund a pension comparable to the State Pension. It would have been better for me to opt out of the NI - which I was assured was funding my Pension - and save for myself if I could.
TLDR: I have been given the impression by various Civil Servants (ie State employees) over the years that I am entitled, yes, entitled, to a full State Pension because I have fulfilled my side of the deal and made full NI contributions all my working life. So, no, I don't think it is reasonable to means test my State Pension, or make any other deductions from it.