Taking a loan for a risky and volatile market is a dangerous business or investment idea as no one can predict the next swing and direction of the market
People take risk even high risk because base on their predictions, the market will go up and give them profit so risk is worthy to take.
that is why we are advised to use our spare cash or money we can afford to lose but a loan is not a money you can afford to lose neither is it a spare cash.
That is true. Using your own money and more important spare cash is safer than borrowing money. It does not mean you will get profit from the market because it depends on other factors but at least, you won't have pressure like borrowing money.
Borrowing money has more pressure because you will have to always think of loan interest repayment, collateral liquidation, market volatility and risk of losing money by the market and the loan position.