Oh give me a break. Professors know that students are applying to medical school, and will require letters of recommendation. This is a perfectly legitimate career choice and it seems that you have a problem with that.
My problem isn't that premeds need letters from professors. Students that choose to go into other fields (eg, grad school, etc) need letters too. My problem is that many premeds seem to feel entitled to getting a letter from any professor they took a class from simply because they did well in a class.
In any upper division science course, there is plenty of opportunity to interact with your professor. You don't even need to do exceptionally well in their course: if you put in the effort, show interest in the material, and actually interact with the professor chances are that they'll be willing to write an LOR for you. In my experience, a letter coming from a situation similar to what I just described would be much stronger than one from a professor you didn't get to know, but got an A from. In this case, the prof can actually demonstrate that they know you.
One of my undergrad profs had it right: in a LOR, they don't want to hear that you did well in the class. They want to know if you're qualified to marry their son / daughter. Many times, if a prof doesn't feel they really know you, they won't write a letter because they have nothing to say.
But let's face it, as for intro courses, there are lots of profs who teach those who hate doing it and only do it because they got the short end of the stick. And even if they do actually like teaching, those classes are HUGE.
As I said, the exception is if you're a not science major and these are your only classes. In that case, you should know ahead of time that you're going to need to do something in advance that will help you get a letter from a prof of a huge class. A cosigned letter from a TA is probably a good call here.
