The server is theirs so they can say what happens on it.  You only use it with their agreement.
You don't have to agree to anything if you don't want to but the alternative is to stop using their server.
As it would be against TOR's reason for living to monitor traffic the choice is obvious.
When I have been in the same situation I have asked for more detail to thwart the problem because it is in both our interests to stop it.  They then are told I have blocked ports which should stop that traffic and they are happy and leave me alone.
I always say my effort is at my expense to help people in need of privacy and that I will do what is necessary to keep the exit going and they appreciate that - usually.

Robert