Open-mindedness should not be fostered because, as Scripture teaches, Truth is great and will prevail, nor because, as Milton suggests, Truth will always win in a free and open encounter. It should be fostered for its own sake.
The world does not speak. Only we do. The world can, once we have programmed ourselves with a language, cause us to hold beliefs. But it cannot propose a language for us to speak. Only other human beings can do that.