This is absolutely true. If you have anything in the form of a hobby, interest or talent you want to nurture, medicine will squeeze it out of your lifestyle. Your family and friends will not see you very often. Spending time with your pets and going on long vacations will also be a thing of the past (unless you're a derm). And when you're 80, almost dead, and looking back, I guarantee that in one way or another, you will wonder if you didn't miss out on a giant chunk of your life.
Also, your idealized perception of "saving people's lives" is an immature view. Thousands of people are in engineering for everything from telecommunications to designing toys and love what they do. Chefs, writers, chemists and optometrists all love what they do, and none of them are directly "saving people's lives" but are affecting people nonetheless. If you chose medicine because of its heroics factor, reconsider, because you're ultimately not going to leave any greater mark on the universe than any other person who made money, gave to charity, volunteered somewhere, or made some sort of impact through their work. 99.999% of the greatest people in the world whom we admire were not medical doctors. And despite your insistence that you're not "talking down" to dentists, your complete lack of understanding that your career is not a determinant of what you will actually do in the world is immature at best, arrogant at worst.