The only anti-Patrick argument that hasn't been fully retorted is why doesn't he borrow fiat at a cheaper rate and convert it to bitcoin?
Why borrow at all? If he's making a narrow profit margin, why does he bother taking all the risk? If he's making a decent profit, why not use that profit to pay down debt?
You could ask why bitcoin mining exists at all because it is essentially marginally profitable and by your logic bitcoin itself doesnt make any economic sense!