When you assess your financial well being, do you only consider your debt or do you also include the things you own? Are you better off with no debt and no IRA or with $10,000 in debt and $200,000 in an IRA?
If you simply considered net worth, then you could be broke, yet buy any car you wanted. Borrowing 100% of the cost of the car would, according to your method, leave you in the same financial situation. That is, zero net worth. Then the first payment would come due. What would you do then? There is a reason the bank wouldn't have given you that loan.