Most workplaces have a least one — Mr. or Ms. Negativity — the person who consistently looks on the dark side and talks about it a lot.

Human resource consultants brand that employee as “toxic.” He or she is someone who drags down morale, hampers teamwork and raises stress.

In a perfect workplace, negative people wouldn’t have been hired in the first place or they’d be fired because they’re more trouble than they’re worth. Right?

Not necessarily.

It turns out that many workplaces put up with toxic behavior for a variety of reasons. Sometimes the negative employee has talents that no one else in the workplace has and is essential to operations, at least for the time being.

Other times, management is more concerned about the potential legal hassle and expense associated with a firing. Could the negative employee make a claim of age, sex, race or other protected class discrimination?

Some companies prefer to wait and hope discontented workers leave of their volition rather than initiate an action.

You might be surprised at survey results reported this month by Fierce Inc., a leadership training and development company. The company surveyed 500 employees through its social media and email channels and asked them to identify toxic behaviors in their organizations,

The largest share, 41 percent, of respondents, ranked negativity as the most detrimental workplace behavior. And 99 percent of the workers surveyed said a negative employee was extremely or somewhat debilitating to morale.

But for the most part, negativity is allowed. A majority of the respondents said they were unsure if the “overly negative” person should be fired, or they needed more information to decide.

Only 4 in 10 thought excessive negativity was cause for firing. And three-fourths of them said their organizations were extremely or somewhat tolerant of toxic employees. In fact, some managers believe contrary expression helps promote innovation.

But, according to Fierce founder Susan Scott, keeping the overly negative employee on board is unhealthy, both to co-workers and the organization.

“There are always going to be individuals who can’t move past their issues for one reason or another, or can’t get out of the victim mindset,” Scott said. “When this occurs, set your organization free and terminate the relationship. It may seem hard at first if their work is solid; however, the havoc they are having on the organization as a whole isn’t worth an individual’s contribution in most cases.”

Scott says workplaces should carefully analyze if they’re doing enough to recognize and reward employees. Feeling undervalued is a big cause of negativity.

Managers also should pay attention to conflicts between co-workers, she advises. Don’t assume they’ll work it out on their own. See what you can do to help resolve the issues. It’s critical to confront the problem and the behavior head on.