(Given that the question was put on hold, I try to ask the question differently. If it is still off-topic I vote for deletion. Still having trouble grasping the question.)
If you know that an institute/department/adviser is looking for new PhD students, but you also know that this institute/department/adviser is really bad for a scientific career (e.g., high attrition rates, few if any get tenure) — what do you do?
On the one hand, no one likes a snitch, people who complain are often seen as bitter and as lacking loyalty. And it might be a question of fit.
On the other hand, there is responsibility to future PhD students (their careers and the other damage bad environments inflict).
There are guidelines for actual scientific misconduct (like plagiarism, fabrication, falsification), but is there anything for this kind of situation?
I see no ethical quandary whatsoever in revealing your own negative experience / suspicions of systemic problems within an academic department. It would be easier to argue that some ethical obligation cuts in the other direction: i.e., people should be informed about what they're getting into.
You don't discuss your current status in the academic community. Of course complaining about people who are in a network of your peers and superiors could have some risk to you. (That's basically always the case.) But that's not an ethical concern. The need to be "loyal" seems a bit misplaced here. Yes, loyalty is good, but it cuts both ways. Some people / an institution had a chance to treat you well, and apparently they really blew it. They can't reasonably ask you to deny or minimize it.
I will say though that complaining is tricky. The problem with people who are bitter enough to complain is that...well, they sound bitter. In particular, your description of this nameless department sounds a bit cartoonishly bad to me: I couldn't recognize it in the context of any of the academic skullduggery I have seen in real life. For one thing, you almost seem to be saying that the department faculty takes an active interest in crushing the dreams of students and postdocs. To be honest, I am skeptical: crushing students' dreams can be hard work, and we are terribly busy. For another, you imply that this department is viewed as exemplary and the terrible treatment and terrible placement of graduate students is totally ignored by your academic community. Really? In my circles (mathematics, US) departments are ranked in large part on how how well they service their graduate students: percentage of students who get through, time to degree, good placements. Some places have a reputation for being "nicer" than others, but even a "not nice" top department does a better job of placing its students than a mediocre one. Or so it seems to me, anyway.
So if you really want to complain effectively, I suggest you take the time to make your complaints factually based. Can you assemble (in a solid, honest way) statistics to show that the department you talk about is bad for students? People will take that a lot more seriously.