In fact, I think a loan can get someone straight into trouble, especially when the borrower and lender have agreed to a repayment contract. So far I'm not interested in any loan, and I hope I'm not doing it for any purpose including trading. Trading should be a way to gain profit and minimize the risk of loss, but if someone feels he is capable and responsible for repaying his loan on time then I never think it's a problem, especially for himself.
Trading swing can go in both directions i.e. you can go up or down. It's very famous saying that "invest as much as you can afford to lose" and borrowed money is something you can't afford to lose. So I m not in favour of investing money that I borrow from someone. If you don't have money simply just don't invest.