Sometimes, it can also be a issue of <i>identity</i> (left/right politician, Java/Lisp programmer…)[1]. If you attack an idea that someone attached to his identity, it will be like you attack his very being. Common reactions can be dismay, denial, or even violence.<p>[1]: <a href="http://www.paulgraham.com/identity.html" rel="nofollow">http://www.paulgraham.com/identity.html</a>