Ubiqutin, I don’t think it’s as simple as you are making it sound. For one thing, it may not be a “black and white” situation. In fact, it sounds like it probably isn’t. There is a definite possibility that someone is not treating someone else in the family they way they should be (and last time I checked, there was no such thing as a perfect family) but it’s not something that warrants police intervention. However, once they are called in, they could create problems.
More importantly, I have known of situations in which there really was no problem and the family was as close to perfect as most people get, but once the police were called in, they created a lot of problems for them.
This may be because the police are human beings and not necessarily the best human beings, it may be Anti-Semitism, or it may be simply because the job of the police is to be extra-cautious, and they are simply doing their job.
But our job is not to be naive, to be aware of the potential results when calling the police and to exercise caution before doing so. That is why there is a halacha of mesira. It is precisely because the secular authorities might not do things the way the Torah warrants.