It’s important because truth is the heart of liberal democracy. The two ideals of liberal democracy are liberty and equality. If your belief system is shot through with lies, you’re not free. Nobody thinks of the citizens of North Korea as free, because their actions are controlled by lies.
Truth is required to act freely. Freedom requires knowledge, and in order to act freely in the world, you need to know what the world is and know what you’re doing. You only know what you’re doing if you have access to the truth. So freedom requires truth, and so to smash freedom you must smash truth.