"He who knows only his own side of the case, knows little of that. His reasons may be good, and no one may have been able to refute them. But if he is equally unable to refute the reasons on the opposite side; if he does not so much as know what they are, he has no ground for preferring either opinion. The rational position for him would be suspension of judgment, and unless he contents himself with that, he is either led by authority, or adopts, like the generality of the world, the side to which he feels most inclination. Nor is it enough that he should hear the arguments of adversaries from his own teachers, presented as they state them, and accompanied by what they offer as refutations. This is not the way to do justice to the arguments, or bring them into real contact with his own mind. He must be able to hear them from persons who actually believe them; who defend them in earnest, and do their very utmost for them. He must know them in their most plausible and persuasive form; he must feel the whole force of the difficulty which the true view of the subject has to encounter and dispose of, else he will never really possess himself of the portion of truth which meets and removes that difficulty. Ninety-nine in a hundred of what are called educated men are in this condition, even of those who can argue fluently for their opinions. Their conclusion may be true, but it might be false for anything they know: they have never thrown themselves into the mental position of those who think differently from them, and considered what such persons may have to say; and consequently they do not, in any proper sense of the word, know the doctrine which they themselves profess."
— John Stuart Mill, On Liberty
And even more relevant to yesterday's quote:
"[The Catholic Church] makes a broad separation between those who can be permitted to receive its doctrines on conviction, and those who must accept them on trust. Neither, indeed, are allowed any choice as to what they will accept; but the clergy, such at least as can be fully confided in, may admissibly and meritoriously make themselves acquainted with the arguments of opponents, in order to answer them, and may, therefore, read heretical books; the laity, not unless by special permission, hard to be obtained. This discipline recognizes a knowledge of the enemy's case as beneficial to the teachers, but finds means, consistent with this, of denying it to the rest of the world: thus giving to the élite more mental culture, though not more mental freedom, than it allows to the mass. By this device it succeeds in obtaining the kind of mental superiority which its purposes require; for though culture without freedom never made a large and liberal mind, it can make a clever nisi prius advocate of a cause. But in countries professing Protestantism, this resource is denied; since Protestants hold, at least in theory, that the responsibility for the choice of a religion must be borne by each for himself, and cannot be thrown off upon teachers.
— John Stuart Mill, On Liberty
Yes, "at least in theory." The same applies to voters who trust political teachers to tell them all they need to know about other views, without exposing themselves directly.