Wikis are community-based projects, where people from all across the world can come together to share their passion for a subject. It goes without saying, then, that you may not agree with everything someone does. The important thing to remember is to assume someone's intentions are good. Most people are part of a community to help it, not to hurt it!
To assume good faith means to assume that someone is making a well-intentioned effort to help the community. Even if they did something you think is wrong, odds are, it might be an accident. Assuming good faith means to assume that there is no intention of malice and that editors are trying hard to do their work for the greater good of the community.
Even if someone made an edit that needs to be reverted, it does not mean that their intention in making that edit was anything less than honorable. You should approach disagreements with a sense that the other person just wants to help, so you can be a friendly, honest, and caring voice in the community rather than someone who assumes that anyone who does something differently than you is out to ruin the project.
When you can reasonably assume that something is a well-meaning error, correct it with a kind, explanatory edit summary, and even leave a message on their user talk page or wall. Don't just revert it without any explanation, and certainly don't label it as vandalism unless it has malicious intent behind it. Letting the users know what they did wrong not only helps them become a better editor but the new messages notification showing them that someone has, in fact, read their edits can be ideal for positive encouragement. Knowing that someone has read what you wrote is a great feeling, one that can get people deeply involved in communities they care about.
All in all, remember not to act as if their mistake was deliberate. Correct them, but don’t scold them. Inform, but don’t intimidate. These are people you want to keep on your wiki, so why scare them off?
Whenever an edit or a message irritates you, take a step back and assume the person is just trying to help. This can help you look past your frustration and recognize what they are trying to achieve, and then act more kindly based on that understanding. Consider using talk pages, comments, or walls to explain your point of view, and invite others to do the same. This can avoid misunderstandings and prevent problems from escalating.
Well-meaning people can take actions the rest of the community feels are unwise, and you should discuss the actions calmly and seek compromises wherever possible. What you should not do is accuse the person of vandalism or sabotage. Foster a culture of consensus, not condemnation.
When a well-meaning person takes an action you disagree with, you should always start with a message on their user talk page or wall. Never go straight to blocking them or protecting a page - and never use admin tools or stature just to get your way in a disagreement. Remember that every action on a wiki can be undone, and letting an unwanted edit or page sit for a short time while you talk with the user and wait for their reply is not a terrible thing.
Of course, some users act in bad faith, and we trust admins to use their judgement and their tools to deal with them appropriately. However, assuming good faith is a powerful tool. Even in cases of obvious vandalism, you might be surprised how often a kind and personal warning can get people to stop, and even apologize. Some vandals are just bored readers who do not think anyone is paying attention or don't believe that their obnoxiousness is affecting real people.
Very malicious cases of spam, vandalism, and trolling are blatantly obvious, and those can be dealt with quick administrative actions like blocking. The vast majority of people are there to help the community, but every once in a while you get someone who just wants to vandalize to ruin other people's good time.
Just remember that everyone you deal with has feelings, and everyone can help you build the community that you love if he or she can be shown that their work is noticed and valued, as well as how they can improve wherever needed. Always do your best to assume good faith, and your reward will be a thriving wiki community!