Hmmm I don't think that's the case at all – if at all, active voice is less clear and "sloppy". (See the examples I mentioned here[0].) But maybe we interpret the term "clarify" in different ways?
You're right in terms of what I meant by "clarify", which was more about writing that looking less "sloppy". The examples I think about aren't ones where the investigators are referring to themselves by "We" but where you're writing a paper about molecules interacting with each other. So something like "A activates B, which in turn inactivates C" reads more smoothly than any of its passive-voice counterparts.
Yes, because there is a clear subject and the fact that one thing activates another is important (at least in scientific papers, causality is kind of the point). Using the passive voice in this case is clumsy and awkward. On the other hand, there are legitimate cases for the passive voice when the subject is unclear/unknown/unimportant. Forcing the active voice then results in the overuse of meaningless pronouns or vague words just because there needs to be a subject. Good writing is using the right construct, which depends on context.