If you want to gamble with money, that's fine - you are welcome to spend any money that you have earned through hard (or easy) work. If you want to take out a bank loan though, you sign a contract which usually clearly defines what you will be doing with it, or at the very least will define certain things that you cannot do with it and near the top of the list is spending it on highly speculative assets. Just look at the mortgage market, banks are willing to give very high amounts over a very long term, because it is backed by an asset that is generally trending upwards with decades of history and evidence to back that up. Crypto on the other hand has only been around for less than a couple decades and had a serious market for about ten years. Maybe at some point in future it will stabilize to the same degree, but that's some way off.
To get loan from Bank one has to full-fill lots of formalities before his loan is approved. You can get loan from bank to buy a car or for mortgage but there are not many Banks around who are willing to give you loan for Bitcoin investment because Banks don't like Bitcoin. Having said that even if there is Bank willing to give you loan for investing in Bitcoin then don't go for that option. Investment in bitcoin is not doubt profitable but over longer duration and there are certain rules and regulation of Bank loans which a borrower has to follow like you have to pay the instalment on time. There are chances that you invest in Bitcoin and price goes down for long duration, then as a borrower you have to pay the instalments along with interest from your pocket.
In countries where Bitcoin is not legal, banks will never provide loans for investing in Bitcoin. If a person takes a loan by showing other purpose, he must think carefully before investing whether he will be able to repay the amount he is borrowing. If he has the ability to repay the loan regularly through his other income opportunity, then a loan can be taken for him. And when investing in Bitcoin, an investor must invest with a long-term plan. In the case of Bitcoin, there is no way to say when the price will increase or decrease. For investment, you must invest with a long-term plan, otherwise the possibility of loss will increase.