In some cases, that is true. In other cases, it is an important part of removing a toxic element from your organization.

There are some people who refuse to behave in the best interests of the group, no matter how much direction you give them.

...but you are correct that they are often only one part of the problem. Then again, often firing them will motivate some of their supporters to quit.

I imagine that was the impetus behind firing Monica, so perhaps turnabout is fair play.