One argument I've encountered that holds water, at least with regards to being unable to discharge student debt: you can't repossess someone's mind. (Technically you can, but that'd be a messy affair.)
Wow, citation please? Credit card companies set up pop-up stands and give away free t-shirts to students who apply for their credit cards. The VAST majority of the applications are happily approved.
Update: excellent citation kileywm. I guess my perception was a bit dated.
"(5) Eliminates excessive marketing to young people. Consumers under the age of 21 must prove that they have an independent income or get a co-signer before applying for a credit card. The Act also prevents credit card companies from mailing offers to consumers under 21 unless they "opt in," and prohibits companies from wooing students with T-shirts, free pizza and other free gifts at university-sponsored events."
As an anecdote, my experience (within the past decade) reflects the parent post's perception. My first credit card had a very low limit of < $1000, and was surely because I was then young, a student with no stable income, and had a lack of credit history.
My first credit card as a student came with a $500 credit limit for what its worth. I wasn't able to get a $5k limit until I was out of school and working in my field and made a dent into my student loans.
Also, the interest will kill you unless you actually plan on declaring bankruptcy, in which case say goodbye to any chance of buying a house in the next seven years.
I would think that in your early twenties, defaulting on student debt and declaring bankruptcy would have roughly the same net impact on your life.