Taking a loan means that you have to repay the loan in any way, and investing in Bitcoin with a loan means that if you cannot achieve success from this investment, then you will not be able to repay your loan. Now the question is, Since you are investing in Bitcoin with debt, Is the success of your investment guaranteed? Bitcoin is a currency thats moves very volatilely, so there is no guarantee that you will succeed here, now that there is no guarantee of success here, then how can you invest beyond your means here? Even with a loan, which you have to return with more interest after a certain time? Making such a decision is definitely very foolish, market fluctuations can cause losses in an instant, and then it will be difficult to repay the loan, so you have to invest with what you can afford to lose, decide to invest from discretionary income.
Talking loans to follow up your investment yet the best decision actually, but it can still be applied in a sensible way, what makes loans a bad thing is when the amount taken is enormous and the interest rate is unbearable. I belong to a cooperative that issues loans at 2% monthly interest rate to it's members.
Let's say for example I invest $100 weekly using DCA and I stumble on a very fine dip, I can go ahead and borrow up to $1200 which is equivalent to 3 months DCA and buy at once, with the view of paying up with the funds intended for buying Bitcoin for 3 months only to pay back the debt and for the interest $72 which I can pay with part the next week's buy amount and continue buying Bitcoin normally. When we go for amounts beyond our abilities and with high interest rates, it becomes a real problem for us since it's never advisable to pay back with our portfolio, else it would be that we're gambling rather than investing.