I have had similar conversations regarding what “good” and “evil” are and find that there is often an overlooked and or misunderstood view of something that is as intangible and dualistic as existence itself. I find that "good" and "evil" are existential constructs/outcomes of that which is and is not. The action and or even intention of something are but outcomes of an expression understood by that which is affected by said expression.
Your exploration of this construct being an attempt at understanding is quite expressive. I too am interested in how a “good” act can be seen as “evil” all the same dependent on view… and this is why I can not pin “good” and evil” to the whole. “good” and Evil” are then but feelings felt by existence by way of reflection- one beings actions onto another and right back again.
As you stated in your observations, an act can be creating “good,” while simultaneously creating equal or far greater “evil.” This is why it is so important to have communication… notice, I didn’t say “good” communication. That which you feel may be right/good as someone is stating something you don’t believe will be pushed away as bad/evil only because one may see it in such a way. Allowing for one to express ones self and not rejecting such expression allows for common ground to be found. A dualistic balance of what “I” am and what “I” am not is existence itself. We can not create or destroy constructs such as “good” or “Evil,” we can but attempt to understand that which is not ourselves as a singularity. Without that which is not ourselves, we would cease to exist.
To those that wish to attempt “good”…I have an option for you. It has been said in many ways, and I am hearing/seeing it occur more and more as people realize the dualistic nature of intention. The construct of creation rather than destructive intention. The action of building up rather than breaking down. Finding common ground rather than starting over moves the whole toward “good.” One moving with such intention tends to that which is existence itself… feeding the growth of the whole and ones personal growth encompassed within the whole. Two halves of that which is, forming that which will be.
I think an action is only as good as its outcome, the intention of an act should not be overlooked as it does hold some importance, mostly toward how you look at the person doing said 'good' or 'bad' act, though there are many areas to approach this problem.
If we look at the language in itself, what the words actually mean, we will come to one sort of answer. Then if we look at the morality and perspective of what good and bad are we come to another sort of answer.
To then get the most accurate answer we would have to workout how those outcomes can be brought together. And each persons opinion will still vary.