I have seen people do this in the past with stocks. Initially it might go well, but the longer term picture definitely isn't that bright. No matter how much confidence you have in the trend or an asset, markets in general can stay irrational much longer than you can stay solvent, hence the reason I wouldn't dare to borrow anything from a bank for investment/trading purposes.
Bitcoin is so small in terms of market cap and illiquid that you don't have to borrow money to make big gains, you just need some more patience and wait for the next parabolic leg up. Witout borrowed money you can just sit back and not feel any pressure to book gains. It's perhaps not as exciting as trading and whatnot, but at least there is so much less risk you are exposed to.