It is sad and true. But I think you underestimate the importance of truly free education, meaning no tuition and grants towards living expenses. It is natural that students from poor or dysfunctional parents are afraid of going into debt, when the mantra in the environment is: "you will be an unemployed PhD". The issue of capturing students from disadvantaged environments is a complex one, and no one factor can change it. It takes a concerted approach to welfare and equality.
The evidence seems to be that the low income students who are most discouraged from the prospect of debt are the low ability ones. However, let’s put that aside for a moment. I wonder if you underestimate effects of upbringing on access to university. That often keeps people out of university before they even get to the point they can apply.
One report I read said that 30% of qualified students in Denmark don’t get into university, so their system would appear to also not be perfect. It did not say how they defined “qualified” but I imagine it would be related to high school grades. However, I would say that the access problems for many low income students start well before then with parents who don’t emphasis the importance of school even in high school.
Compare this to the newer “open access” universities in BC. Open access refers to universities that students can get into with only a minimum performance in high school. New Zealand also has such a system. I worked in the New Zealand system and it was horrible. However, I now realize that the problem there was that the funding system made universities so desperate for students that they were under pressure to keep students enrolled no matter how bad they were. In BC, the situation is different as the Open access universities are prepared to accept very high attrition rates in first year. Thus, students who, for whatever reason, would not have gotten the grades in high school to otherwise be considered “qualified” for universities sometimes actually do prove that they can handle it. Often they transfer to the more traditional universities after a year or two. My experience is that they are often better than those who got accepted directly into the more traditional universities.
I am not that familiar with the Danish system but I suspect that these students would never make it into Danish universities as it would be too costly to accept them given the low probability they would survive first year. Thus, the ones that do have potential would be wasted in that system.
My basic point is that I don’t think it is always straight forward to determine which system is most likely to “waste” potentially good low income students.