Yes, clearly that’s an example of when it interferes with clarity. The point is that–either way–simplistic (dogmatic) application of strictures (e.g., Always avoid the passive voice, etc.) isn’t going to lead to better communication. Compare:
A) The subjects reacted positively when the researchers gave them the placebo.
B) The subjects reacted positively when (they were) given the placebo.
There’s no reason to chose A) simply because the subordinate clause is in active voice, and B), in fact, is more economical.
Well, yes, that’s what I mean above by “discursive reasons” for creating better cohesion.
One can’t just use single, isolated sentences (or clauses) as examples if you want to demonstrate why one should choose active over passive (or vice versa). When you string together a series of sentences, sometimes the passive becomes a better way to keep focus on the important ideas. This is because certain verbs are semantically preferable, but they also happen to collocate with subjects that are semantically distracting for the particular context at hand.