I believe my department is failing to enforce standards in doctoral examinations. How to proceed? I have witnessed multiple doctoral examinations at my (top-10 rated) university in which the student did not, in my opinion, demonstrate the required level of knowledge and understanding under questioning but was awarded the degree anyway. The committee consists of the advising professor, usually one or two additional professors (one of whom may have been a co-advisor), and the professor that chairs the doctoral examination committee in the department.

I suspect that the degrees are awarded at least partially out of expediency because failing the student after admitting him/her to the examination would be unfair to the student and indicate a failure by the advisor and be embarrassing to both, especially because the examination is open to the public (so other students as well as friends and family are present). 

In addition, I believe that choosing one examiner to be a co-advising professor is a blatant conflict of interest, since failing the student would also amount to a failure of the co-advisor and is therefore not in his/her interest. The third examiner is sometimes selected by the advisor strategically from a pool of  current or former collaborators.

Finally, I get the impression that the chair of the doctoral examination committee defers to the recommendation of the advisor and does not serve as an additional arbiter of standards for the department (as I assume would be his/her duty), again out of expediency, because if he/she did refuse to sign the departmental forms, it would create a conflict and presumably a lot of additional work.

I know I'm not the only one who feels this way about the situation, but so far nobody, to my knowledge, has spoken out. I'm inclined to speak out anonymously because I find the lack of enforcing  standards to be embarrassing and sickening, especially given the rating of my university. Speaking out, even anonymously, could create problems for me, which is why the best way forward is unclear to me. 

Does anybody have any recommendations about how best to proceed? Are my expectations unrealistic? 

Edit: One commenter asked me to be more specific about what I thought they lack. Briefly put, they all struggled to answer questions about the problems they investigated. These questions required nothing more than a fundamental understanding of the relevant physical processes. Some of the required understanding is part of MSc courses and would not have been acquired as part of the PhD research itself. What troubles me is that rather than continuing to question the student, the committee members seemed to be going out of their way to give clues and avoiding pushing the student too far in the sense of making the deficiencies too obvious.
Yes, I have seen some similar things in my life and this is indeed a very tricky question. There is a strong tension between our ideals regarding the quality of PhD's (and other degrees) we feel our institutions should be awarding and the practical realities on the ground, which involve messy and awkward decisions that have a direct influence on people's lives. This reality is such that sometimes we feel we have no choice but to compromise our lofty ideals to some extent. As long as the compromises are small, this is probably as it should be, but when the compromising reaches alarming levels, it is reasonable to start becoming seriously concerned.

What I would suggest is this. First of all, it may be worth remembering that the behavior you are describing is not your doing nor your responsibility. The chair and the members of the doctoral examination committee are the ones who are making those decisions and putting their own reputation and credibility behind them. So, although you find the behavior concerning and perhaps for a good reason, you cannot reasonably be expected to fight all instances of poor decision-making at your university. Thus, one option is to simply do nothing except to resolve privately that if you ever preside over a doctoral examination yourself, you will follow your conscience and let the chips fall where they may, and thus play at least a small role in making your department and university better.

If you want to be more proactive, an honorable course of action would be to actively pursue the role of chair or member of the doctoral examination committee so you can put the goal of raising standards directly on the agenda. Or you could strive to be appointed to the departmental committee that decides the makeup of the doctoral examination committee, and thereby help get people with high standards be placed on that committee and help prevent the kind of conflicts of interest you are describing. Through such behavior you will be setting a personal example and showing that you are not just criticizing others but willing to take action yourself for the goal you believe in. Since you mention that you believe others in your department feel the same as you, you may find that you have a good number of allies who will support you in your mission, and even your opponents will respect that you are acting on your convictions. Of course, it will take time and effort to bring about change, so be prepared for a long struggle ahead.

Finally, if your position within the department does not make it realistic for you to seek the kind of active, visible role I suggested above, or you are unwilling to make such a large effort to see change happening, I don't have much to suggest. I don't think there are easy fixes; someone will have to do the work to change the culture of your department. If it's not you, maybe you can work behind the scenes to identify more senior allies willing to take on that role. You might get lucky and find someone passionate enough about the subject, but probably you won't.