Yeah, I wouldn't be so hard on people who found they really disliked medicine by the time they're done with residency.
First of all, people are notoriously bad at predicting what will make them happy in the future. (See Daniel Pink's book on the topic.)
Second, even in the US system, many start their educational paths to medicine while they're young and for many kinds of wrong reasons, including parents, perceived prestige, perceived amount of money earned, and the well-intentioned but nebulous idea of "helping people".
Third and most important, nobody really knows what it is like to be doing medicine until they're in residency. No amount of the unspokenly required clinical volunteering or shadowing will give you the idea before applying to medical school. Once in medical school, people start getting some clue on their clinical rotations, which is why we see such a shift from "wanting to serve the underserved" on their medical school applications (which may have been entirely sincere at the time) to wanting as little patient interaction as possible (thus choosing rads or anesthesia), choosing "the least medicine" medicine (psychiatry), or pragmatically choosing to make a bank while still having a life (derm). But nobody really knows what it's like until internship when it's too late to quit because of the medical school debt etc. Medical education is kind of a trap: people don't really know what they're getting themselves into until it's too late.
I have the benefit of being a "non-traditional" ie much older and having a decent prior career that I switched from, so I did quite a bit of soul searching before applying to med school. I did not even once regret going into medicine while in med school, and now in psych residency not only have I not regretted going into psychiatry (yet), but I'm loving it so much I'm reassured of my choice even on the crappies days I have on psych. However, my medicine rotation was such a miserable meaningless grind for me* that, if that was what my whole residency and future job were like, I would f^*^*//*&#$ quit.
* - hopefully I didn't offend any of my medicine colleagues. Obviously internal medicine is super important, and I have a lot of respect for you guys and your work, and I completely understand that this work may be fun and enjoyable to some people (though categorical medicine interns on that rotation were just as miserable as I was), but it is an exhausting meaningless grind *for me*.