It's impossible to run the kinds of controlled large scale socio-economic experiments you describe. If we ignore the evidence that doesn't meet your high standards, we'll have no real world data.
There's things you know, things you don't know, and things you think you know but you don't know. It's the last one that harms the most.
> If we ignore the evidence that doesn't meet your high
> standards, we'll have no real world data.
I would also add that variable standards of evidence are a good way to allow your strongly cherished beliefs to remain unchallenged for a long time.* No comparison with other countries, and their respective policies.
* No data on where these students graduate from, or in which subjects, or with which grades, or what their average salary is X years later, or whether they'll actually be able to pay back the loan.
It's missing a huge amount of important information; you really can't justify the conclusion "tuition fees are good" from this alone.