If you go to sufficient depths, the definitions of all words become of questionable
The words in the phrase "do no evil" are different only for the fact that in the case of the third word, 'evil', you do not have to go to any depths at all to realize this.
The phrase "do no evil" has no useful, objective meaning. What it does have is subjective meaning.
"Do no evil" is not a slogan.
It wasn't designed by Google's marketing department to present the essence of the company to the outside world in as few words as possible.
"Do no evil" is more akin to a mantra.
It is used as a keyphrase by those who make decisions to focus their minds on the vision they have for the company, and on their own set of guidelines on how to realize that vision.
While the word 'evil' is incredibly simple and useful within a strong context (such as one's own mind), it is useless and unnecessarily confusing in a weak context (such as communication with the outside world).
(It is unfortunate that in the corporate world of today one has to hack some mindspace before doing anything else; to focus extensively on what *not* to do first, in order to be able to focus with clarity on what to do.)
If "do no evil" is internal use only, how come it has been used externally as well?
Google's "do no evil" represents a decision-making system which is a sort of internal achievement for those who employ it. "See? I'm honest with myself." It is natural to wish to share one's achievements and joy with others.
With "do no evil", the decision makers at Google show us a piece of themselves in an attempt of sincerity.
As far as I'm concerned, Google does no evil while I perceive their decision makers to be self-honest.
When I perceive that greed, fear, and short-sightedness have eaten away their ability to be honest with themselves, with regret I'll say they fucked themselves up.
You are welcome to trust or not trust Google (or whomever or whatever you wish) according to your perception, and also to proclaim things evil or not evil according to your own moral inflexibilities (even if it is of not much use).
Objectively, it's a moot point.