Agreed, but... You always "have to sell it". If your strategy is to always buy BTC (or you are earning BTC), you probably have some costs, unless you are living a 100% self-sustained life, grow your food on your property, ...
If you have fiat to spend, it means, you have not bought BTC with that fiat.
So if you earn 100% in btc (if you get fiat, you convert it to btc), then you always have to sell it sometimes. I just think that selling btc is way worse option than using it as collateral. You end up with much better position than by purely spending fiat. And that's true even if you got hacked/rugpulled, because as the btc collateral appreciates, you withdraw it.