Seriously, I feel this way all the time. I get very frustrated when I encounter people who don't agree with me, to the point that I've developed the habit of never ever discussing anything "contentious" unless I'm with someone I know holds the same views--or a good friend with whom I can communicate and who isn't too emotional. The frustration for me comes from lacking the knowledge to back up my opinions. If I felt like I could refer to all the exact sources that have led me to my opinions, I'd be willing to fight with people head on. And it's not like these people are referencing exactly where their opinions come from. But often, I'm dealing with people who are at least as ignorant as me, often more, and who also argue with so much emotion that I just don't dare engage.

When you're in a situation where you really disagree with someone, maybe you can express that without necessarily inviting a heated argument? Like "I have to say I really disagree with you, but this is a contentious subject and I'd prefer to stop the whole discussion."

For myself--there are only a few subjects about which I feel very strongly. I try to be educated about them. Once you appear knowledgeable on a subject, people often back off.