One might think that the open forums of social media would lead to more participation in discussion about hot topics like politics, religion and security. However, a report by Pew Research Center shows just the opposite: social media users don't like discussing controversial subjects.

Pew calls this the "spiral of silence," which is a tendency to keep opinions to oneself, particularly when the topic is controversial.

"Some social media creators and supporters have hoped that social media platforms like Facebook and Twitter might produce different enough discussion venues that those with minority views might feel freer to express their opinions, thus broadening public discourse and adding new perspectives to everyday discussion of political issues," the report says.

Pew surveyed over 1,800 adults and focused on one particular issue: Edward Snowden's allegations of government surveillance on American citizens' phone and email records. Pew selected this topic after finding a variety of opinions about it. This particular survey asked people about how willing they were to discuss their opinion, both in person and on social media.

Pew's results showed that people were less likely to discuss the Snowden story online than in real life. However, people were more willing to share their opinion if they thought their audience shared the same stance. This applied to both on and offline.

Interestingly enough, though, the spiral of silence extends to offline for heavy social media users. They were less likely to discuss their opinions in person, as well.

These findings indicate that Facebook and Twitter were not seen as adequate discussion forums for those wanting to express an opinion on the Snowden story.

There are probably several reasons for this silence. First, most social media users don't want to get into arguments with their friends, most of who are really only casual acquaintances. Online arguments have a way of escalating quickly and also open up users to trolling and harassment.

Social media users are probably also leery of posting opinions online for fear that their bosses or future employers will see what they've posted, affecting their jobs and careers.

Many would argue, though, that the fear of offending others, stifles public debate, and that this report is cause for concern.

"A society where people aren't able to share their opinions openly and gain from understanding alternative perspectives is a polarized society," says Keith Hampton, from Rutgers University, who assisted in the study.