I do understand - I just don't agree.
Many young people see their deductions going to pay for things they don't believe they will get. My own children both pay into occupational pensions, but don't expect to get a state one. Someone who can't afford large payments, or whose employer pays in the minimum will know that their old age is likely to be far less comfortable than that of their parents.
We also paid high interest rates when we were young. We locked into 16% at one point, as we had two babies and thought they could rise even higher. I know what it was like. But house prices were not as high comparative to earnings. I think I am about 15 years younger than you? When we went to apply for a mortgage (full-on interview, with 3 months' payslips in hand) we were allowed to borrow twice one salary and half the other. Nowadays that would equate to about £90k, which would not come close to being enough to buy an average house anywhere in the country. Therefore FTBs have to save for a much bigger deposit or borrow at a much bigger multiple. Even with lower interest rates that is a burden. Also, low rents are a thing of the past, so those who are renting have less to save. In our day it was more common for people to marry younger and not to live together first, so it was easier to save. I blame the sale of council houses for that - the stock of reasonably rented housing sent right down, and landlords could hike the price of rents, which affected both private and social rents.
I may not have statistical evidence of people paying more into pension funds to save on tax - how could I have? - but do you have evidence that it is not happening? I doubt it. People (rightly) don't have to declare their motives for doing what they do, they just do it. We are both speaking anecdotally. You haven't heard of one person who has cut hours to save tax. I have - my neighbour, a hospital doctor who has dropped to half time as her income is only marginally reduced by doing so - in fact the drop in take-home pay is less than the cost of childcare for the days she is now at home. Similarly I know people at the other end of the salary scale cutting hours because of tax credits. I know personally of a friend's daughter who will not increase her hours as keeping them as they are entitles her to top-ups, and she would have to spend on childcare if she earned more. She is a graduate with a lot to offer in the workplace, but the system means that both of these women (at least while their children are young) are better off not working full-time and the tax they would be paying is lost to the economy. The doctor will be able to make up for list time far more easily than my friend's daughter, who has made no career progression or paid pension contributions. She at least has an education to fall back on, but many in her position won't, and are destined to remain low-paid workers who rely on benefits in older age. It does happen, but our personal experiences prove nothing either way.
Also, I am not saying that people get pension credit easily. I do understand the system - just not the figures at which cut-offs and means-tests kick in. I am saying that for those on low incomes it can be galling to see others having a better standard of living because they didn't pay in, just as it can be for low income workers to see people on 'gateway' benefits getting more than they do after a full week's work.
None of this is anyone's 'fault', as I keep saying. The system needs an overhaul. I am not suggesting that pensioners (at any level of pension) get too much - in fact I think the state pension is too low - but I understand young people thinking that they won't get one in their turn. They probably won't, unless we have a radical change in the system.
We now have a low-wage economy, and tax credits have pushed many hard-working people into benefits dependency. This is wrong, IMO. It benefits governments, who can tinker with top-ups and decide who gets them, but it is detrimental to the recipients, who have their agency and choices reduced.