Bernie Sanders didn't just "offer people free stuff". With regard to the fact that student loan debt is owned by the federal government already, that it is fabricated completely out of thin air, and that it is the largest single debt in the history of humankind, there would be no harm in relieving our society of the burden of debt.
The results would see massive economic growth actually, as student loan payments on average are not $250 but closer to $600-900 for any jobs that pay at or above living wage. Most people under the age of 40 list student loan debt as either the primary or one of the primary factors in not having children, vacationing, or owning a home. This clearly shows that the debt burden is really hampering economic growth in a serious way.
Not to mention that college is literally free in most countries, and attendance rates are roughly the same. Just the same as they have healthcare, retirement benefits that aren't just self payed, and public transportation. Those are separate issues, but never forget that debt is completely made up by someone to control other people using INTEREST.
I highly recommend reading David Graeber's book Debt.
Edit: a quick note; the student loans debt is also due to the massive deregulation of colleges and their administrative bloat. Coaches at schools make millions, while professors make less than living wage in many cases. To add to that, the total student loans debt as of March 2023 was greater than 1.75 trillion dollars, while the total GDP of the US is 23.5 trillion. Thus student loan debt totals to 1/20 of our total GDP. The outstanding balance and interest rates will drive this higher without relief, and default will be the obvious solution.
America has also been going through a large, but undocumented, brain drain. Many upper middle class and wealthy college educated leave the country, as the government cannot pursue student loans from overseas earnings when the earner makes less than 125000 dollars a year in salary alone. This means that many Master's and PhD recipients simply leave and never pay their loans, which are eventually defaulted and then forgiven anyway.