Bitcoin Speculative Attack
In this video I talk about Pierre Rochard's famous essay on speculative attacks on bitcoin.
By borrowing in your local fiat currency and buying BTC with the proceeds, you are actively helping to increase the money supply of your local fiat and thereby devalue it against bitcoin, which has a fixed maximum supply.
If you can collateralize these loans with things other than bitcoin, such as houses, you can also avoid the margin call problem.