Wikipedia:Why you should be nice to people who vandalize
There are many reasons why you must be nice to those who vandalize. One reason is that they may in fact become a constructive contributor. They may even become a wikifriend. Another reason is it sets a good example, at least for other people, if not the person who is vandalizing. The last is that it might actually be a legitimate edit. It may have been a mistake on either end, or maybe the person you’re dealing with simply didn’t know wikipolicy, or maybe they knew and forgot. Ultimately, it’s because they're not just vandals, but people.
They may become a constructive contributor
One reason why you should be with those who vandalize is they may become a constructive contributor later on. They may realize what the heck they were doing at one point, and turn around. Warnings might be enough to ‘rehab’ a few, or even some of them, blocking them, RfC’s, and arbitrary committee rulings may help others stop and think about what they are doing. That's why Wikipedia has the above in place. We all need help contributing at one point. Vandals may need help learning how not to be vandals, and the above-mentioned is a Wikipedian way of doing so.
To set a good example
Another reason is to set a good example. Here in Wikipedia, nearly all social interactions are public. I notice one thing about people who vandalize is they watch people very, very carefully. I’m sure on some level, at least in the beginning, they are saying “Hmm. These people are really nice.” Even if the overt behavior doesn’t change, it may help them become more willing to contribute constructively. Also, other people are watching you. Some of these people are new to Wikipedia. Nobody may realize it, but everyone’s behavior will be affected by your own.
It may not be vandalism
The last reason is the fact that the edit may not be vandalism at all. It could be a legitimate edit! Another reason would be a new person who is honestly ignorant of policy, or someone who merely forgot it. The first reason is best made up by giving an honest apology by whoever was guilty. The remedy to the latter two is to gently remind the person to heed policy next time.
Remember, they're human
One last thing I want to say is those who vandalize are human beings. They have feelings just like you and I. They make mistakes, just like you and I. They can learn, just like you and I. They are inconsistent, just like you and I.
There are many reasons why you must be nice to those who vandalize, and now you know three of them. They might contribute constructively later on, you need to set a good example, and the edit may actually not be vandalism. In the end, they’re actually only human, and so are we.