Making it harder to get a student loan is hardly "outlawing" anyone from going to college. Schools would still give scholarships. Plus, tuition would almost certainly go down. Right now they can charge as much as they want because banks are will to lend whatever colleges charge. If all of a sudden people stopped buying their product when they raised the price too high then tuition would come back down to what it was only a few decades ago.
Even if fewer people ended up going to college it wouldn't limit opportunity. If anything it would likely make it easier to get ahead. Fewer jobs would require a college degree - there wouldn't be enough applicants who have one - and we'd likely see alternatives to college become more popular and widely respected, which would give high school grads more options for how to get started with a career.
If you want to limit the cost of college then doing it by putting caps on how much a university can charge could be a more straight forward option than hoping costs come down by limiting loans to those who can't afford the cash option. (e.g. If a university wants state funding then they need to cap their student costs) Even then - loans would still need to happen for people who can't afford much more than their basic housing expenses (if even that - think about kids who get kicked out at 18).
You're speaking in a lot of "if market forces behave the way we all think they should thanks to basic econ like supply and demand" but that's not how things always work in the real world.
Considering ~50% families don't have any retirement savings and don't have an emergency fund, do you really their kids are gonna be able to afford all the expense things associated with college? (Remember - these people just got out of high school! They have likely never had a job and have no money at all)
Regardless if job requirements change (they only will for a subset that no one cares about and no one is trying to get), you're going to screw people over. The lag time between no-loans and job-requirements dropping is going to be too long. There will be a lot of people who fall into the cracks and will be stuck with the lowest tier jobs because they couldn't afford a cash-only education until it was much less expensive.
Regardless of this - I feel like this is the wrong approach to debate lower costs vs no loans vs whatever-where-a-student-pays-in-the-end. I think 4 year college should be free (no tuition, books paid, stipend or special housing, etc.) given how the world works. I went to college for free due to CH 35 of the VA and it was really the only reason I was able to do it and fully commit to it. I have no problem with having a more educated populace - regardless of what they study. I did study something that came with very gainful employment but that wasn't obvious in the beginning of my studies. I think 4 year college would be less necessary if we had better education from the start - but we're never going to get there in this country.
That varies so much by student and to bar a whole class of people out of these things is not going to improve their outcomes. While some students are not served with better employment opportunities by going to college and earning a degree - there are many others who are.
Outlawing things to a group of people isn't going to serve them better. It will mean that the entire middle class will be unable to educate into jobs. Educating them about the effort college requires to be successful once you leave would be better.