That's easy to justify. If you pay your loan off more slowly, then you pay more interest. No different from, if you pay your mortgage, or a loan for a new car or something off more quickly, then you pay less interest. (Though I do think the interest rate on student loans has been too high in recent years. Ought to have been reduced to match, maybe the inflation rate. I guess this year that's not an issue though!).
The difference compared to any other loan though, is that you don't know what you are earning at the start (and the rate of interest, I'll pick that up later):
Also according to here:
Free UK 2026 student loan repayment calculator. Forecast repayments for Plan 1, Plan 2, Plan 4, Plan 5 and postgraduate loans with salary projections, interest breakdowns and comparison tools.
www.studentcalc.co.uk
The level of repaid debt is quite a lot different (this is in today's prices, so any total repayments greater than the loan amount have cleared what they were loaned):
Someone with a debt of £45,000 earning £42,000 would pay back £71,000 and still have about £22,000 "cleared" at the end.
Whilst someone with a debt of £45,000 earning £75,000 would pay back £59,000 and be debt free after 12 years.
Whilst someone earning £39,000 would also pay £59,000.
The above figures are in today's prices and assume someone leaving university in 2021. I have also made no changes to the base assumptions (for example RPI is 3%). They also assume the debt is the value now (in reality there would be a small difference in the amount due at the end of the course to reach this point, however for sake of simplicity I've assumed that neither had had a job until this point).
As it's in today's prices you can see that unless you're earning less than any of the above numbers you'll still be paying back more than you borrowed (i.e. the government is actually profiting from your loan). With the government benefitting from the person earning £75,000 less than the one earning £42,000.
Also RPI plus 3% is quite a high interest rate, this is the same as my mortgage provider's SVR (well technically that's BofE base rate plus 3%, i.e. few want to be on that if they have any option) yet without the risk associated with lending a mortgage (someone defaulting with their house in negative equity).
It's harder to find variable rate loans in any other area, which makes other comparisons harder to make. However likewise there's few loans which last more than 5 years, so arguably other loans aren't that useful as a comparison.
As someone in a rate of pay which is above the average for someone with a degree, I'm happy that I'm not saddled with a student loan to repay.
If I was on £40,000 my take home would be about the same as someone with a degree on £42,000. However the higher my salary guess the bigger that has gets, If I was on £67,500 and still have about the same take home salary as someone with a degree on £75,000. (I've used those rates at they are the rates I've used in the illustration near the start of this post).
Given that not having a degree hasn't slowed my earning potential by much, but I benefit from those who do have degrees (including those who have taught me, medical care, etc.) it's not unreasonable for me (as my rate is pay could allow me to do so) to be subject to a slightly higher rate of taxation.
Someone of an age where they had benefited from a degree but had been provided with a grant, the above numbers show that they are likely to be quite a bit better off than those with a loan earning the same over their career.
As time goes on, there's going to be more pressure to change towards a general taxation route as more and more of those who benefitted from grants retire and so the number of voters such a change would would result in higher costs would reduce (although many would have kids who then benefited from not having higher costs).