You can commit evil accidentally, without being evil, so, you're dead right "Don't be evil" is a weaker instruction than "Do no evil". Accidental evil is allow

You can commit evil accidentally, without being evil, so, you're dead right "Don't be evil" is a weaker instruction than "Do no evil". Accidental evil is allowed for Google, so long as it's an unintended consequence. That said, their motto is a lot better than most!