The real point of the interviews is ritual. It is immaterial and impossible, really, to discover if you are concealing anything if you are adept at such and have the scores to back you up as a decent candidate. I know people on the high end of the sociopathy spectrum at HMS and bizarrely awkward individuals at Penn. Everyone knows, too, that many interviewers themselves have personality defects that range from mild to downright inhibiting. When I embarked upon this process, I thought that to be a physician was to be extremely well-put together, with poise and composure, strong social skills, a sense of dignity and compassion, and a sharp mind to go along. It just so happens that, while such people exist or get quite close, there are gross exceptions to this standard everywhere you look--from the lowest to the highest levels of the game. Whether such exceptions are themselves the rule, I do not know, but I know it that the real situation may come close to it.
In the end, there is no such thing as a perfect medical school candidate, and everyone has their flaws. If they were to winnow out everyone who wasn't a fanatic about medicine, 100% psychologically perfect, or top range score-wise, they would have scarcely any candidates left. Just bear in mind that this process is a ritual: it is there to make certain that you understand the game, that you can play it, that you will not trip up on it, and that you understand what this game requires of you.
That in itself is quite the accomplishment, I believe. If you can convey it, you are set. Whether you understand it as a game, or have a less cynical view is immaterial. What matters is what you can convey. There is no reason to be negative about this process. Just see it for what it is. It is important to see whether you are the right kind of stuff to begin training.
I have a surgeon friend at a top school who tells me that interviewing is itself a kind of training. He says that the point at learning all the canned responses isn't that you lie to the interviewer. It is that you internalize what medicine is about. The transformation process is slow and uncertain at first. But from primary application submission to interviews, this process has changed me, and, I believe, made me more "doctorly." His explanation makes the process make total sense to me. This process is supposed to be difficult. If it were not, admissions committees would not be getting what they want.
All this said, I think MMI would be a fantastic supplement to this somewhat haphazard process. I think it would make things more efficient and fair. I do think, on the other hand, that MMI interviewers should all be trained well. Not all schools' MMIs are equal, and I think medical schools should look closely at selecting and training MMI interviewers.
To be quite candid, too, medical school interviewers do not make the best interviewers. Sorry but they don't. In my late 20s, I can clearly see how much of a difference socially the years have made a difference. Medical schools should keep the medical students as tourers idea. I have met some of the coolest med students that way. But medical students for interviews seems inappropriate to me, and I'm surprised that this practice is so widespread.