Borrowing is a financial instrument of choice. Sometimes borrowing can make you particularly financially strong. Not long ago, a Bitcoin investor I knew borrowed $1k to buy Bitcoin. At that time, Bitcoin was going through a price decline. Although his reasoning was that he would hold Bitcoin for the long term. Moreover, he had engaged in Bitcoin accumulation DCA strategy. He tried to increase his holdings by buying additional Bitcoin. Later he paid off the loan from his alternative own sources but during the bearish period the additional Bitcoin buy increased the size of his portfolio. And he remains steadfast in his long term goals.
I gave this example to show that if you have a source of timely repayment, it would be great and smart to increase your Bitcoin holdings by borrowing during bearish periods.
I think it is never right to take a loan to invest. As you said, if you can repay the loan along with the investment or on time, it is never a good and wise decision to invest with a loan. Because if you do not have money at this time, if you invest aggressively with a loan, then it may be difficult to maintain continuity in your investment later. For example, if you invest with a loan, then you will have to repay the loan and to continue investing, you will move away from the continuity of investment.
Yes, you can invest with a loan in one way. For example, if the market has fallen, you have money to buy aggressively. But you have kept your money in the bank but your bank account has been locked for some reason. In such a situation, you can invest with a loan if you want. But you have to know exactly how many days you can repay the loan in between