What is wrong with loans?

It isn't loans that got us (US) in trouble.   It was the unbridled emission of credit to unqualified borrowers.  In our current fractional reserve system, each loan creates more money.  Even the fractional reserve lending isn't what got us in trouble, although it was a contributing factor allowing additional leverage that we're still hiding and unwinding.

A bitcoin loan should include interest, which is just the risk adjusted time value of money.  The borrower would need to qualify and have a way to pay back the loan.  The inability for borrowers to pay back the loans, combined with the leverage added to the system, combined with the ratings agencies being co-opted by the banks to hide the risk is what led to the near-failure of our financial system.  I'm not convinced the problems have been solved.

What bitcoin brings to the table is a algorithmic check and balance which prevents fractional reserve banking.  You can't lend $10 for every $1 deposited.  You could lend 5 BTC for every 5 BTC saved and the incentive to do so would be an interest rate commensurate with the risk of the borrower defaulting.  If our banking system had run on a one-to-one ratio of depositors to borrowers, and proper credit checks, there wouldn't have been a problem.

I'm a proponent of Bitcoin precisely because the problems have not been solved, but rather cleverly papered over and hidden.