Hi op,
You sound very down and pessimistic and I think people are being unnecessary harsh accusing you of 'stealing' a university place. I bet a lot of people criticising you for saying you can't pay back your student loan went to uni for very cheap fees or even free.
The thing is you've picked a very competitive notoriously difficult course. It's supposed to be hard! Also you are surrounded by smart capable people. It really skews your perspective. I worked in acamdeia for a few years after uni until everything in my life imploded and I had to leave and got a boring admin job with staff with a much wider range of abilities. It really opened my eyes, I thought I was fairly useless at uni and only did well because I worked crazy amounts, turns out a lot of my social circle were extremely intelligent and had had a head start in study habits for various reasons.
A lot of jobs don't require much brain power and they won't fire you if you can manage to turn up on time and your seen to be trying. Obviously I'm not talking about being a barrister here, I'm talking about something that you don't need a degree for. And the way the economy is now there's no shame in taking a job that isn't a graduate job. It's still useful to have a degree, even if you start at the bottom the degree has taught you a whole bunch of life skills as well as educational skills and it'll help you move up the ladder once you've got some experience under your belt.
Uni is also so unlike employment , you are unlikely to ever write something as long as an essay ever again, you will never have to memorise a bunch of stuff just to write it down in 4 hours then forget it later. And you are unlikely to be working in such isolation or have the pressure of grades again. I have a friend who dropped out of uni and was a bit rubbish at it, bad grades, last minute assignments and missed loads of lectures etc... but he's great at his job because it's easy he knows exactly what to do and he knows he has immediate consequences for not turning up, so he's never late !
You've got onto your degree now, please don't focus on the future so much, focus on doing as well as you can in it. And you are an adult now, you don't have to rely on your parents permission for things. Push those boundaries as much as you want! They can't physically stop you from volunteering and there will be loads of opportunities to do it through uni.
It's your life now, think about what you want from it. There are jobs like you describe and there's no shame in packing boxes in a warehouse if that's what you want after uni. Why not apply for temp work doing that in summer to see how you go? But don't agonise over that now. Focus on how you want your life to be over next year both on your course and daily life and see how you can make it that way.