It takes courage to have an open mind. You cannot know in advance what new knowledge is good or bad unless you consider it. That doesn't mean that you must embrace all new knowledge...it merely means you must consider/evaluate it.
A guarded mind is a fearful mind...and a closed mind is an empty mind.
BTW, you cannot fight an enemy you cannot define/know. And you cannot define/know your enemy if you are unwilling to consider what he is and what he believes.
I strongly disagree.
A truly open mind is a sewer, or a garbage pit. It contains anything that anybody chose to throw in it, for reasons good or ill, with no effort to assess the content. An open mind is a lazy mind.
Your post is internally contradictory. Read it carefully.