Alceste,
You are perfectly correct regarding the distinction between factual claims and imperatives. The Pope's statement was not that the usage of condoms make the problem worse. I hardly think his statement implies that the individual use of condoms fail with regularity. Rather, he was speaking of the distribution of condoms and said that they make the problem worse. It seems fairly clear to me that he had something in mind like the reports of Dr. Green, who himself is speaking of the affects of condom distribution (in truth or in error). In the view of the Pope, condom distribution is linked with and creates a mentality towards human sexuality that works against its containment.
Now, its certainly fair game to say this is a wrongful observation and support that with contradicting evidence. Nonetheless, we know that they are some professionals saying it. I do not reckon that the Pope is lying through his teeth, but sincerely believes, if from flawed studies (a point on which I myself remain unsure), that condom distribution has had an effect that works against its objectives.
I myself think it is possible that there is some merit to Green's analysis. Have there not been even cases here in North America where sexually spread infections of various kinds have been massively on the rise, even as the availability of condoms has become so widespread?