Do you think dangerous people should stay alone or will isolation make them more dangerous?

Some people are very violent in relationships and end up killing and hurting/beating their spouses. Do you think that these people should stay out of relationships and public gatherings or do they become more dangerous when isolated. There are alot of people that don't function well in public places where they start yelling or start fights. I've seen so many cases and I have no idea why these people are not kept away from functioning society. Why aren't there patrol officers to make sure such people don't disrupt society cause there are many.