It's not really a good idea to invest using a borrowed money because the outcome is uncertain. However, if you have other source of income to cover the losses and pay the loan just incase everything didn't turned out well then it's up to you if you're willing to take risk. This is solely for investors who have a back up plan, aware of the risk and prepared for the worse case that might happen.
I would say like you. Completely banning crypto investment/trading through debt is not entirely correct. Because I have been in debt first in trading. Lucky I've returned that within a year. But there is a note that we must understand that it is better to invest using the free money you have. Investments in the form of debt will increase the burden on you. But if you already have good management skills, go for it.
I used to be in debt for trading because I felt confident in my abilities and it worked. I used to go into debt and bought BTC around 2016 and from that money I got 0.36BTC. After that I can accumulate more than that and return the debt.