Good and evil would be entirely subjective, and while there may be statistical data supporting what is generally considered good or evil (I don't know that there is but it is something that could be sampled), there can always be mitigating circumstances at play that can override opinions regarding an act.
If it is only a human definition then 'evil' would always be a deliberate act requiring knowledge that the act was evil, or intentional ignorance to avoid knowing the result (this, of course, assuming that such was entirely subjective). If 'evil' is the result and not the opinion, then the act would be as bad whether knowing or unknowing.
I know I 'qualify' some things as good or evil that are different than what others do, and it isn't unusual for me to use a religious understanding to do this. The reason is that if I solely leave it up to me I can consider some very terrible things as 'good' and easily qualify them under such headings as "for the greater good of mankind" or "ends justify the means" type considerations. Conversely, I can easily see such things as the modern day welfare and social programs as insidiously 'evil' where I assume that most people think of them as charity and 'good'. I judge that from both points of view and not by the intention but instead by the effect and results over time and in the future. The things that are simplest for me to scale are things like intentional prolonged suffering, where one deliberately draws out the fears of a 'victim'. These things I can easily qualify as evil -- as I am sure that most would -- but would everyone? I know that people can become numb/sensivite to their ability to judge these things, if solely left up to the individual, and so I wonder about that too.
Excluding any religious faith precepts from the agreed-upon subjectivity of the concepts of "evil" & "good", you've raised a ponderable point. That is, that sometimes a "good", (e.g., beneficial), result can stem from an "evil" cause and other times, an "evil", (non-beneficial), result can arise from "good" causes. While both "beneficial" and "non-beneficial" are also matters of subjective perspective, what I'm getting at is that such
'cause & effect' chains are extremely convoluted. One cannot accurately predict the outcome(s) of a mixed chain of events, (which includes both
beneficial and
non-beneficial circumatances, (like wars, for instance).
For example, prior to WWII, no one could have predicted that both Japan and Germany would eventually come out of
losing that war in a beneficial way, (both rebuilt and obtained stronger economies than before the war). During the prosecution of the war, those suffering from it did not consider the war to be a "good/beneficial" thing, (nor did they immediately after the war). Eventually, some "good" came out of what was considered to be something "evil". The same idea can apply to less dire circumstances, (e.g., running late for work because of a flat tire ["non-beneficial"] and missing a 12-car pile-up on the route normally taken to work ["beneficial" to the late worker, not to those in the accident). The foregoing example emphasizes both the subjective nature of the human concepts of "evil & good" as well as the 'mixed chain of events', (where those concepts alternate and/or blend at times).
The conclusion that I draw from such considerations is that "evil & good" do not exist as 'black & white'
precepts, but only as subjective concepts. As such, apply those concepts involves making subjective value judgements, (which harkens back to my contention that we all judge since we all make such subjective value judgements; concerning "evil & good" and all sorts of other matters). If one can justify/substantiate their value judgements with rational reasoning, then these judgements would hold water. Conversely, if such value judgements have no such basis and are based instead upon subjective
precepts and a personal preference for irrational basis, then that bucket leaks like a sieve.