A lot of people ask questions like "How should society be organized?" or "What should be done with criminals?" or make statements like "There shouldn't be censorship in the world" or "We should have a world without violence". All these thoughts show a fundamental misunderstanding of morality.
Moral statements can't be made without specifying an agent. You can say "I should do this", or even "you should do this", but you can't just say "this should be done". The only meaningful way to interpret such a statement is "each involved person should work together to achieve this", but that statement is forgetting that each individual involved has different information and a different perspective, and so assuming that the right action from your position must be the right action from everyone else's position (as the passive voice requires) is wrong, because it's possible for two completely good and earnest people to disagree about what "should be done" (and I'll give some real world examples at the end).
There would be some instances of violent conflict in a world with only very good people. Due to varying information, two good people could have opposing duties in such a way that they'd have to fight and neither of them would be in the wrong. I call this situation "the moral conflict". (Some freeloading situations are a non-violent example of moral conflict.) Protagonists would understand this and take it no further than the subject of the dispute was worth nor harbor any hard feelings over it, but I can't say the same for non-Protagonists.
To give a non-real-world-politics-infected example of a situation where the moral conflict would be taken to the point of violence, consider two good people trapped in a cave and knowing when they'll be able to escape but having only enough food for one of them to survive that long. The moral course of action (for either agent) is to try to save whichever of them they think is more strategically important to the forces of good. In most cases, this will be themselves, as they're very likely to have at least some disagreement in how a person should act, but obviously both people think they have the right side of every disagreement. So if they both understood the lesson of this article, they'd fight to the death in complete good spirits and without any anger between them. (We're discounting the risk of this resulting in both of them dying.)
Abortion is the most common context this is ignored in real life. Tons of people say things like "If you think it's immoral, you don't have to do it, but you do you and I'll do me". That's right; if you think I'm murdering someone, just don't participate and stop complaining. (Nevermind the fact that they are forcing you to participate by funding it with tax money...) A lot of "you're not the one doing it so it's not your decision" arguments rest on this, including the ones people make against violent vegan activism.