Are acts judged "good" or "evil" based solely on the intention of the actor?
Evil is not working together to make the world a better place
End of quote
I rather agree with this. But it's got a few potholes. If you claim sole knowledge of the definition of what makes the world a better place, you do so at the expense of others who think *they* know what makes the world a better place. And that isn't "working together." So what is the missing element? Tolerance of differences.
In order for all to work together to make the world a better place, you can't write off an entire group of people who might have different ideas than you do (ubiquitous 'you') - that's the exact definition of not working together. This is the struggle I see between groups that hold different philosophies today.
Let's suppose someone agrees with that statement so I can proceed with the logic. In order for groups to have tolerance of each other's ideas - for the purpose of "working together to make the world a better place" - they will have to suspend their beliefs as being critical to the work. All beliefs without objective (testable and verifiable) evidence are subjective. Therefore, governing actions for making the world a better place based on any religious or philosophical untestable and unverifiable idea is "evil" by your definition, because it sacrifices the equally subjective, untestable, unverifiable ideas of another group for the sake of your own.
It is not easy, as a Christian or a Muslim, for example, to suspend the rules of "rightness" that the Bible/Quran teaches. These forums (and do I need mention the entire world?) are full of intolerance of differing ideas, and I infer that the people that are intolerant would be very satisfied if everyone would change to their way of thinking. This is not working together. It is therefore "evil" (by the above definition which the OP agrees with.)
I often think that people don't believe we can work together unless we all believe the same thing first, and so the current push is to eradicate all other beliefs first, and then we can "work together." In the same way that Jesus points out that if you expect a gift in return for giving a gift, then you haven't really given a gift in the first place, this argument is fallacious. In other words, it takes no special moral fiber to be tolerant of people who agree with you hook, line, and sinker. It is far more noble and giving to express tolerance of those with whom you disagree. Thus, tolerance of people who have different beliefs is integral to "working together" and anything else is "evil."