to be honest i think that you should never borrow bitcoins or money at all, because if you will borrow bitcoins you will have to give back much more because they are greedy
i think that if you very need loan then only for trading, when bitcoin price is large to sell them and then buy them again when they are cheap again to give back and get some profit
But you can really take out the fact that we need bitcoins to invest and what happen if we see good oppurtinity that we can surely get more benifits if we invested with it? Their comes that we need to borrow so we can have money to invest and thats good since we used our barrowed money for such good instance and surely we can pay our debts when we get our profits and surely we can earn more for that.