If you are in a discussion with people sharing all the same opinion, you do learn more arguments fortifying that belief and take things as facts. From there on, it is rather complicated to be open minded.
People with opposing thought or information always illuminate a topic from a different point of view. The exchange of thoughts -- if you allow it to happen -- show your strong and weak points in that discussion. Thereby, you will always learn more, more than just black and white, more you have ever thought about, and -- maybe -- that you were wrong.
We take too many things as facts, share radical opinions too fast on facebook and turn down anyone that thinks different (yes, Apple's motto). Maybe we are too close minded or too lazy or too affraid to allow people to challenge us?
I think we learn the most about ourselves when we have to talking and interact with people who hold opposing ideas from ourselves. If you only talk to people who have the same ideology, then you will never truly question your beliefs and see if they are valid. You need opposition.
If you went through life and everyone had your same opinion you would never learn anything new because you would never have to. When people bring other opinions you see things differently and it is at that time when you typically are able to learn new things in the world.
Likely, we learn far more from people with opposite opinions and views than our own. The fact of the matter is that people with the same opinions only enforce our current views. That means we learn nothing new from these individuals in most cases. We need to interact more with people that have differing opinions than our own.
We learn less from people with opposite opinions of our own. This is because our bias does not allow us to listen and learn from anything the other person has to say. In fact people learn much more from people with similar opinions. This is because we are willing to sit and listen to them.
I'd love to say that what we learned as children is true, and do believe that people with open minds learn from those with opposite opinions. In reality, brain scan studies have show this is the opposite of the case - people actually actively try and explain away contrary or oppositional data