I definitely agree with this. I should definitely be prepared to answer these kinds of questions and it might be good to include in the secondary if given a proper chance. However, the primary should be why I want to do medicine not why I chose not to before.
I get that, but I don't think its so black and white for everyone. Some people become physicians to be involved in medicine as well as other non-traditional paths. I was very interested in public health (still am) and got mixed signals as to whether it would be proper for me to pursue medicine. I've since learned that medicine and public health is a great mixture, but I couldn't tell that at the time with the advice I was receiving. I've learned the mistake in my decision making and I have done so in a way to has strengthened how I could see myself as a physician interacting with my interests and passions to their fullest extent.
Again, I'll understand if I get the harsh treatment you describe (I certainly expect it for some schools), but I wouldn't be coming back to medicine if I didn't think that I'm doing so with clarity and purpose.