“I have never in my life learned anything from any man who agreed with me.” – Dudley Field Malone
Most of the time, we like to be around people who agree with us. We love to feel right, and being around people who think we are presents a perfect opportunity for justifying this feeling. We find it easier to bond with others who think similarly to us, because it minimizes the potential for conflict.
The problem is, it also limits the potential for growth. Sometimes, we don't realize we're wrong until our ideas are challenged. Being exposed to different thought processes and beliefs can reveal flaws in our own thinking - and while it can be an unpleasant feeling to be wrong, once we recognize that we're wrong we can start looking for the truth.
On the other hand, if you're right about something, how can you ever really tell until your idea has been tested against the wrong ones?
The point is not that we need to become more convinced of our correctness - we're often far too sure of this as it is. The point is that, in order to pursue truth, you must know where your beliefs hold up, and where they do not, and be willing to admit that to yourself. After that it's only a matter of following and acting on those beliefs.