>>700396its a matter of security
before you can prevent this from happening on a voluntary level, you can wall off, only communicate with the agressive people carefully
in the process people should be educated on why those people are exactly bad, without inducing sense of fear or telling them to "just stay away"
then when possibility arrives, integrate them.
if someone is trying to replicate the behavior, its sign of will to communicate and should be answered with its demand, maybe it has something to say, it can be either a message of explanation of the situation and how to fix it from his side, or maybe your side, since you are not god and so shouldnt shoot up his messengers
in short, you should be open to people, but not insecure.