I agree because there is no guarantee that you will make a profit in trading currencies always go up and down so there is risk involved. Taking out a loan means creating a financial burden you have to repay the loan regularly with interest. If the investment fails you may be burdened with debt and cannot repay the loan on time that is why we think taking out a loan for bitcoin or any other investment or business is very risky. You should only invest the amount of money that you are prepared to lose.
Although, it's not ideal to consider taking loan for business or investment but it's more manageable in business than taking loan to trade crypto. Either way, you should know that you're into a big risk and in the end you have to repay the loan whether the business is profitable or not. Some businesses require funding to thrive and one may decide to take a loan in order to boost the business depending on how well and good you're in the business but to compare this with crypto trading is actually absurd. Success or profit is not guaranteed in either business or trading but at least business is less risky compared to trading where you have no control over the market. I don't even think banks would lend anyone money when they put trading as the purpose of loan.