>Except minors don't have contractual capacity, for exactly the very reason that they can't understand what they are signing.
They can understand the simple contract far better than an adult can understand the average legal heavy contract. Any reasoning to not give contractual capacity to a minor (especially one who is able to read/write) applies just as well to the average individual.
No, a child does not understand that owing a billion dollars means several lifetimes of debt that they will never pay. If no reasonable adult would agree to the terms but a child would, that immediately indicates that the child is not functioning as an adult and is therefore not contractually capable. Because this can pretty much be generalized to all minors, it's simply laid out in law that they are not contractually capable.
>No, a child does not understand that owing a billion dollars means several lifetimes of debt that they will never pay.
They do. They only agree because they realize it would never be enforced. Maybe a really young child wouldn't, but a preteen would know similar amounts as an 18 year old. That said, most 18 year olds don't really comprehend how much it will take to pay back their college loans and many, once they figure it out, say they wouldn't have agreed. There are also many who take out pay day loans not realizing how bad a deal it would be who would not have taken them had they understood the true costs.
>Because this can pretty much be generalized to all minors
There is nothing you can generalize between a 2 year old and a 16 year old that couldn't also be generalized to someone 18+.
So I'm not really sure what your standing point is anymore. You yourself admit [0] that children and adults don't have the same contractual capability. Your example relies on a ridiculous presumption which exactly proves why minors are not considered capable. And now you're on to people regretting financial decisions, to which my response is, who doesn't?
The information is there, if they do the math. Failure to crunch the numbers is, in my opinion and in the law's, not an excuse to void a contract. Changes like credit card statements showing the results of paying only the minimum payment only do the math for you, not relay novel information. They are only valuable in the sense that people can no longer not do the math and remain ignorant, because it is already done for them.
They can understand the simple contract far better than an adult can understand the average legal heavy contract. Any reasoning to not give contractual capacity to a minor (especially one who is able to read/write) applies just as well to the average individual.