People disagree all the time, but not all disagreements lead to the same levels of stress.

Even though people can be passionate about their favorite sport teams, they can argue about which basketball team is the best without destroying friendships. In the workplace, co-workers can often dispute strategies and approaches without risking a long-term fallout.

Political conversations, on the other hand, seem to have become especially challenging in recent years. Stories of tense Thanksgiving dinners and of Facebook friends being unfriended have become commonplace.

Why does this happen?

Our research – and related research in political psychology – suggest two broad answers.

First, our work shows that divisive topics – issues that are polarizing, or on which there’s no general societywide consensus – can evoke feelings of anxiety and threat. That is, simply considering these topics appears to put people on guard.

Second, research on moral conviction by psychologist Linda Skitka and her colleagues suggests that attitudes linked to moral values can contribute to social distancing. In other words, if someone considers their position on an issue to be a question of right versus wrong or good versus evil, they’re less likely to want to interact with a person who disagrees on that issue.

An automatic trigger of anxiety

In our research, we define divisive issues as ones that don’t have a clear consensus.

For example, just about everyone supports food safety; but if you bring up issues like abortion or capital punishment, you’ll see people fall into opposing camps.

People also like to have a general idea of where someone falls on an issue before they start debating it. If you’re talking with a stranger, you don’t know how to anticipate their position on a divisive topic. This creates an uncertainty that can be uncomfortable.

With this framework in mind, behavioral scientist Joseph Simons and I designed a series of studies to explore how this plays out.

In our first study, we simply asked individuals to look at a list of 60 social issues (ranging from safe tap water to slavery) and estimated what percentage of people are in favor of that issue. Participants also rated how much they would feel anxious, threatened, interested or relaxed when discussing that issue.

As expected, people thought they would feel more anxious and threatened when discussing a topic that was generally considered more divisive. (Under some circumstances – such as when people didn’t hold a strong attitude on the issue themselves – they did feel somewhat more interested in discussing these topics.)

In a second study, we investigated the experience of threat at an unconscious level. That is, do divisive topics automatically trigger anxiety?

We conducted an experiment that was based on the psychological finding that people don’t always recognize the source of their emotional responses. Feelings that are evoked by one event or object can “carry over” to an unrelated judgment. In this study, we presented participants with a popular topic (for example, supporting veterans), an unpopular topic (high unemployment) or a divisive topic (stem cell research). They then saw a neutral computer-generated picture of a face and had to quickly rate how threatening the face appeared.

Participants were more likely to see a neutral face as threatening if they were thinking about a divisive topic. (Unpopular topics showed a similar effect.)

A third study replicated these effects using fictitious polling data about direct-to-consumer drug advertising. We told some participants that there was a high public consensus about support for this sort of advertising, and we told others that there was wide disagreement. Specifically, we told them that either 20 percent, 50 percent or 80 percent of the public was in favor of these ads.

Participants then imagined discussing the issue and reported how they would feel. As in previous studies, those who were told there was more disagreement tended to feel more threatened or anxious about the prospect of discussing the issue.

‘Right and wrong’ adds a layer of complication

An additional social obstacle goes beyond mere disagreement. Consider two individuals who oppose the death penalty.

One person may think that the death penalty is morally wrong, whereas the other person may believe that the death penalty is ineffective at deterring crime. Although both individuals may strongly support their position, the first person holds this attitude with moral conviction.

Research by Skitka and her colleagues highlights the social consequences of these “moral mandates.” When it’s a matter of right or wrong, people become less tolerant of others who hold the opposite view. Specifically, individuals with stronger moral convictions tended to not want to associate with those who disagreed with them on certain issues. This social distancing was reflected both in survey responses – “would be happy to be friends with this person” – and even physical distance, like placing a chair farther away from a person with an opposing view.

Of course, no one is ever going to agree on every issue. But it’s important for people to learn about where others are coming from in order to reach a compromise.

Unfortunately, compromise or consensus is more difficult to come by if people start out the conversation feeling threatened. And if individuals feel that someone who holds an opposite view is simply a bad person, the conversation may never happen at all.

In the end, it doesn’t matter if you’re talking to a stranger or friends; the possibility of exclusion or avoidance increases when a divisive topic is raised.

There’s no easy solution. Sometimes raising these topics may reveal irreconcilable differences. But other times, a willingness to approach difficult topics calmly – while truly listening to the other side – may help people find common ground or promote change.

It might also be helpful to take a step back. A disagreement on a single issue – even a morally charged one – isn’t necessarily grounds for discontinuing a friendship. On the other hand, focusing on other shared bonds and morals can salvage or strengthen the relationship.

Melanie Green has received funding from the Spencer Foundation.