You're going to grow my ego with that sorta talk
That's a good question...
I guess it really comes down to two things, education and how much the employer values their employees. The heart surgeons extra pay is compensation in a sense for slaving away in school an extra decade. The other thing is that people are paid for skill, as you said. That's not to say that our aforementioned garbage man and McD's employee aren't skilled, nor are they lazy, but its to say that their employers view them as replaceable. A heart surgeon is a bit harder for a hospital to replace, the company wants to retain him. Furthermore, it requires more money to train a heart surgeon than a garbage man or a McD's employee. As I said, garbage men do have an important job, and I honestly don't think McD's employees are fairly paid (seriously, why don't fast food employee's have unions yet?) but I still maintain that the heart surgeon should be paid more.
On your final point, I guess people aren't really paid based off their value to society necessarily, although that plays a role. Many factors culminate to define wages and so on.
Thank's for bringing that up. I'd never really considered that question. It goes back to my belief that discussion isn't about winning, but it's about having your beliefs questioned, and learning why you believe them in a more deep and complex way. And, of course, how to defend your ideas. So keep messing with them (because this 18 year old is such a master of parenting XD)