Do you think a 17 year old is capable of making that decision?
You're not legally allowed to drink at 17 and you can't vote at 17. But you think it's fine and dandy to suggest to a 17 year old that they take out, on average, 26K to pay for a degree which in the vast majority of cases they don't actually know what they're going to do with? The information given to teenagers is obviously going to biased - schools are their main influence and they actively encourage kids to go to uni because it boosts their reputation.
Unpopular opinion since the demographic of this site is younger than me - but I joined TSR 9 years ago as an A-level student and used it throughout my degree. I've been through the system and come out the other side with clarity because of what I and my friends have experienced and I choose to share my opinions for the benefit of people who are 17 right now who might wish "if only I'd known" in 10 years time.
17 year old's should not be deemed adult enough to take out a ~£26K loan from a government owned organisation when that very same government deems them too immature to drink or vote at the same age. Are you really okay with that level of governmental hypocrisy? And no I'm not pointing fingers at the Tories - they're all as bad as each other since when I went to university Labour was in power ('Education, Education, Education' and 'We want 50% going to university'
and when I was IN university the Lib Dems tripled the fees. When you make that application to university you have zero clue of what you're getting into.
Once you commit to that degree you commit to debt and a one way ticket - you cannot retrain in another degree level discipline unless you have a rich family or as my university career's adviser suggested to me ''win the lottery" (or work like a dog, save and secure NHS funding like I actually did). Nor can you retrain in anything lower than level 6 since you're not eligible for funding. Quite the commitment for a 17 year old.
I'm telling people something for their own benefit - makes no difference to me as to whether they take it on board or not because I've already experienced the negative side of it (graduate unemployment and underemployment) and have come out the other side. But I'm a minority in that sense - you hit your mid-20's and look around and you and see that your fellow arts grads are still working in Asda or claiming JSA/having babies before they've got a steady job. Very few are doing anything 15K+ or grad related.
As for your last sentence - we do pay for it under the current system when we start earning enough to justify re-payments - I've no objection with that. I disagree with a grad tax as proposed in the OP because it's not income-contingent.