> although I suppose one can argue that this is of niche interest, that the bulk of new treatments come from new discoveries protected by patents, and that the interest in medicines covered by expired patents has only been rekindled by improved technology and techniques to better understand their action.
That's actually a problem because you can patent a new treatment based on an old medicine. Several companies did exactly that, unfortunately. But yes, it's rare.
>But still, I feel that a specific justification of patents, along with the privileges they afford, is missing.
It's simple - no-one in industry would be doing drug research without possibility to get at least some profit. And right now it's simply not possible without patents.