If, as claimed by its members, Opus Dei is simply a religious association in which each man is free to pursue his own line of thought, how do you explain the widespread belief that Opus Dei is a monolithic organisation with well-defined positions in temporal matters?

I do not think that that opinion is really very widely held. Some of the most authoritative organs of the international press have recognised the pluralism of the members of the Work.

Undeniably, however, there are people who maintain the mistaken opinion you mention. It is possible that some of them have propagated it for reasons of their own even though they know it to be false. In many other cases it may be attributed to inadequate knowledge. Being initially ill-informed, it is not surprising that people who lack sufficient interest in the question to enter into contact with Opus Dei and receive firsthand information, attribute to the Work as such the opinions of a few members.

In any case, no one who is reasonably well-informed about what happens in Spain can ignore the reality of the pluralism to be found among the members of the Work there. I am sure that you could easily cite many examples.

Another factor may be a subconscious prejudice engendered by a one-party mentality, in politics or in spiritual matters. People with this mentality want everyone to think the same way as they do, and they find it difficult to believe that there are people capable of respecting the freedom of other men. Thus they attribute to Opus Dei the monolithic character of their own groups.