“Truth and freedom either go together hand in hand or together they perish in misery” [Fides et Ratio §90].
The Lord Jesus says that the truth shall make you free. One easy manifestation of the contrary is to be found in the case of the man who is an inveterate liar. He has to keep track of every lie he tells to anyone, to make sure that they are all in sync, lest his deceit be exposed. It’s an impossible task, and it’s why habitual liars usually get found out. Meanwhile the burden of trying to keep up with it all becomes a form of bondage. But the honest man has no such difficulty: by simply telling the truth, he doesn’t have to keep track of what he has said at all. He is free in that sense. I suppose it’s unlikely that JPII had this sense of things in mind when he wrote the quotation above in FR, but I think it’s an interesting example of the truth of what he said (which is really no more than a gloss on Jn 8:32).
It seems likely that a case can be made that a sort of bondage likewise arises from philosophical error, but I’m not sure that I’m equipped to be able to make it. I suppose it might go something like this: a philosophical error constitutes a deviation from the way that the world really is. If a man doesn’t recognize the error, or if he refuses to do so, he is effectively attempting to live in a world that doesn’t exist (at least with respect to his error). I imagine one form of bondage related to this is the intellectual energy that must be expended in order to prop up the error, or in attempting to “bend” the world to fit it. Now this might be less of a big deal in the case of small errors, but the task gets more serious when the error is bigger—in other words, if it’s of greater consequence.
That sounds a bit (or maybe a lot!) like I’m saying that the truth is easy, and maybe that very fact exposes a weakness of my approach to the question. Easiness and freedom aren’t the same thing.