> how would you prevent everyone from getting expensive schooling and then immediately declaring bankruptcy

If the expensive schooling works, then the person should be able to get a nice, well paying job and pay off the loan over the next 20 years. Many of the differal programs (i.e. "putting the loan on hold") programs and policies would prevent this. It's when the clock runs out, and the student can't get the high-paying job that we have issues...