I don't see how this could be stressful even if I continue paying some small amount into my 50s - from my point of view it's not debt, it's more like paying a water bill each month.
For example; a starter salary of £28k would be only £7k over the threshold and "only" result in repaying 9% of that, or £630 per year. But in Austerity Britain people on that kind of salary (e.g. nurses) are already starting to resort to using food banks.
Weigh up the alternatives, such as an apprenticeship or a job offer and university starts to lose ground to other options; but much more so for people with a lower socio-economic background. This is the problem.
Some people will look at the associated debt issues and decide it's not worth it (open question as to what percentage). Often this will be in comparison to a job offer or apprenticeship.
There will also be people who don't look at the issues directly, but instead rely on the guidance of older generations, and perhaps contrast things like living costs.
These decisions are made differently based on socio-economic status. That's the access issue.
I don't have objective data but there's plenty of anecdotal evidence around of people from lower-income backgrounds making choices because of their background not because of their ability.
https://www.theguardian.com/education/2015/aug/17/teenagers-...
From a policy perspective that kind of long term debt comes with stress, health problems, productivity problems, social mobility problems.
Peoples ambition (and in some cases sense of entitlement) comes from their upbringing; if you add long term debt to that aswell you end up in a situation where even more careers are decided by childhood circumstance, rather than potential.