Opposition

No one likes it when they are wrong. That is why we have so many arguments nowadays. Personal opinions can turn people into something nasty, though they can also unite people. It all comes down to what you say (or don't say). Sometimes, expressing your opinion to someone that opposes your opinion will just cause them to hold on to their own beliefs tighter partly because they don't want to be proven wrong. Personally, I don't mind it. I don't like to drag out unnecessary arguments. However, there are those topics where neither side can be right or wrong, at least for the time being.
For example, global warming. Some argue that humans have an impact on it and something should be done to prevent it. Some argue it's just part of nature. Even still, there are some that argue that it's not even happening. Research has implied it's just a natural process that happens regardless of what humans do. But let's say we didn't know that. These sides will argue on whether or not humans should do something. This is a tricky situation. It's impossible to know what is right until it's too late.
Here's another slightly different scenario - communism vs. democracy. This has caused wars. The United States believes that democracy is right. So, back during the Cold War era, it wants to spread it to other countries and prevent communist reign. But why? Why does everyone need to be democratic even if it's against that country's will? That just creates more enemies. Vietnam is one of them. The Soviet Union is another. Just because the U.S. believes democracy is right doesn't mean they need to force others to accept the same ideals. Let the people choose what to believe. Even though they have different beliefs, they can still be allies as long no one shoves foreign ideas down their throats.