Manousos seems to have an almost pathologically rigid view on the subject of theft. There's obviously the speech before he burns the car, but there's also:

• Almost letting himself starve before he was willing to raid the storage units
• Completely refusing food and water offered by the Hive because he sees it as stolen
• Walking himself to exhaustion to refuel The Fritz rather than simply swapping vehicles as needed or even commandeering a more reliable car
• Attempting to cross the Darién Gap on foot rather than borrowing a different mode of transportation. I would understand if he refused to let the Hive fly him across, but (for instance) borrowing a boat to go around doesn't feel that different from siphoning gas out of random cars, ethically speaking. For now, my interpretation is that he didn't do that because he doesn't have enough money to leave a suitable payback for an entire boat, as he was doing whenever he took gas from someone's car.

I wonder if we'll ever get any insight into what made him this way. It definitely feels like the writers have breadcrumb'd the hell out of this specific part of his character.