It's not only about high interest or other banking fees, the thing with market is you can not predict it at all, specially in short-term.

Let's say if you bought Bitcoin now and market turned totally bearish after that and you're in around 20-30% loss then, what you're going to do next?, Bitcoin probably is going to reach $60k or even $100k in long-term but can you really wait for that to happen which could take years when the money you invested was borrowed to you?

And don't ever forget that the stress that it will cause for you since you definitely did not invest what you can afford to lose and you actually did the opposite of that and with every single percent that Bitcoin goes down after you bought, so will your debt.