I used to teach small groups. I had a student who was mentally and sometimes even physically dangerous to the others with their* disruptive behaviour. It was a hard decision, but with my mentor we chose the less harmful option, remove the person from the group and offer them therapy to let them return to the group as soon as possible. It took a bit more than half a year. Due to privacy and other legislations I cannot tell more about this story, but I have to say: unfortunately there are cases when you have to consider this option.
* I intentionally don't want to say if he or she.