I'm going to get straight to the point: the internet is a magnifying glass for the Dunning-Kruger Effect. Many of you may know what this is; basically, it's an effect observed in a study conducted by Justin Kruger and David Dunning at Cornell University. Basically, the idea is that incompetent people will overestimate the level of their skill, and underestimate that of others.
The internet, being a place where you can anonymously interact with people from all over the world, naturally attracts folk who just want to be heard. I think this can be dangerous, and encourage people to develop an exaggerated sense of self worth, where being right is more important than actual learning.
So please, question yourself; when someone has an opinion that you want to resist, examine it carefully before you throw it away. Overconfidence doesn't really beget self improvement.
"One of the painful things about our time is that those who feel certainty are stupid, and those with any imagination and understanding are filled with doubt and indecision." Bertrand Russell