I don't understand the "implicit norms of loyalty to one's employer" reasoning at all, because I've not worked at a place with that sort of reciprocal employmen

I don't understand the "implicit norms of loyalty to one's employer" reasoning at all, because I've not worked at a place with that sort of reciprocal employment. My Dad did ... until a private equity bought his company in the 1980s when I was a teen, fired people, cut salaries, split up the company for parts, and profited on employees still being loyal when it wasn't reciprocated. That said, there's problems I have with this specific sort of employment, where people work ~50 hours for what should nominally be 80 hours (for two jobs) or 120 hours (for three jobs) and don't tell their employers about it. 1) Who controls the work product? My contracts have a work-for-hire clause saying they get copyright for materials I generate while they pay me. How does that work if two employers are paying me salary at the same time? This wouldn't be theft, but it may be copyright infringement. 2) If you have two jobs, both providing health insurance, then how do you handle coordination of benefits if the health care administrators at your companies don't know it's an issue? If you tell each company that you will be using their insurance for primary coverage, the rates may be different than if you designated one as primary and the other as secondary. This isn't theft, but may be a financial loss due to your dishonesty. 3) For some jobs there are exposure safety limits. If you have two jobs, with exposure in both jobs, and don't tell both your employers about it, then you may have health problems from being overexposed, which leads us back to #2. This isn't theft, but still a bad idea. 4) Or, consider more common workplace issues like repetitive stress injuries. If you have RSI and the health&safety officer wants to provide appropriate care, like shift your responsibilities to have less typing, do you keep your other job secret by not talking about the other 20+ hours week where you type? If you keep it secret, and the company spends money on inappropriate care, then that's still not theft, but it is a financial loss due to your dishonesty and worse health outcomes for you.