I think the entire comparison between MD and JD is sort of pointless because the only thing which both have in common is that they are classified as professional doctorate degrees. Within the fields themselves, the skills and personalities required to succeed in both are inherently different. Do you see failed premeds become lawyers, sure, but that doesn't mean they become a successful lawyer.
The perception of doctors are skewed by the media and the entire altruistic part of the medical career is also exaggerated. Coming from a family with both parents as MDs, and a sister as a third-year med student, I can tell you that the salaries represented in the chart and the lifestyles attributed to physicians do not represent the majority of physicians.
The average physician does rounds, teaches a little, reviews patient charts, and fills out forms for prescriptions, and attends faculty meetings. So in effect, being a doctor, is in no different from "another profession". You are paid for your medical expertise which is the compensation you receive for incurring debt for going to professional school. In fact, most physicians are so involved in their work, that they lack the ability to converse on other topics besides medicine. In order to be successful in medicine, you have to involve yourself in it, and that is the cost you pay for being named a Dr.
Likewise, the "saving the world" motto for physicians is also skewed because the ones who are actually experience life vs. death situations are not necessarily internists. These are people who've gone through 4 years of college, 4 years of medical school, 1 year of internship, 2-8 years of clinical training, plus another 2-5 years for specialization. So in effect, the reason why they are so heavily compensated is because they went through 15+ years of training after college. The salary along the way is nothing extraordinary until you have finished all your training. The amount of work these people have put into accomplishing this requires dedication, and as such are rightly deemed to be respected. However, your average practicing attending physician in a hospital does not see these ER type moments unless you actually go for these fields.
Not to mention that the demand for these super-specialties (neurology, invasive cardiology, anesthesiology, etc) are much much lower than internists, and pediatrics so the number of positions available for training and hospital positions are much smaller making them hyper-competitive to obtain. While the compensation may be upwards of 300k, if you normalize the salary by the amount of hours they work, you will see why people say medicine should not be undertaken for the money.
It's also obvious that in a LAW SCHOOL forum, you will see more pessimistic posts about going to law school. Go to a medical school forum and you will see the same type of responses. There are always people who are stressed out and regret going to professional school. It's actually ironic because Lawyer/Doctor may be perceived as the most prestigious fields, but only the lawyers and doctors themselves are involved in the fields to understand the negative aspects of pursuing a career in one position.
At the end of the day, you choose a career which will be economically valuable, and pursuing a professional degree is an economical decision which considers non-monetary factors as well. People who pursue a JD for money will be dissatisfied, just as likely as people who pursue a MD for the money. However, that doesn't necessitate that one is superior to the other.