I have been in a position of hiring and firing for 20 years, in small firms. During that time regrettably I have fired three secretaries for having a negative attitude.
First of all I explained how their attitude was upsetting other staff, and suggested how they could change, and gave them time to do so, but, in the end, I did ask them to leave.
We were a small and cohesive workforce, everyone cheerful and willing to learn and to turn their hand to whatever was needed to make things run smoothly, whereas each of these negative people, in their own way, had a knack of upsetting the applecart, by being miserable and complaining, no matter how much people tried to support them and help them out. Other people had to take on thei extra work burden whilst these women swanned around making excuses for why they couldn't do a full day's work, bad-mouthing the other staff, and generally creating a bad atmosphere.
As I was the person who had initially hired them, and knew their credentials, I was very disappointed to find that even though they had proven abiliity, i.e. good skills, efficient, and turning out good work, they caused disharmony to such an extent that their behaviour became intolerable, and quite inappropriate for the workplace.
Each of them was very shocked to be asked to leave, and two of them were quite threatening, but I would rather have been taken to court than put up with the miserable atmosphere and tension which they engendered on a daily basis. In the event, none of them did take me to court, and I hope they learnt a lesson to take to their new jobs.