Let's say I'm a college graduate (with accompanying student loan debt) and you're a high school grad. We both get jobs at the same company and you're paid 40k while I'm paid 60k. If we both get raises to 70k, I am still stuck with my student loan debt while getting paid the same as someone who did not need to spend years in school or take on student debt.
But why would the other person's salary affect you?
Because of the reasons listed in my original post. If I had to sacrifice time and money to graduate from college to qualify for a job and an arbitrary raise provides the same compensation to someone who does not have a college degree, it devalues my degree. On top of that, besides the degree getting devalued, I still have the original student debt amount.
But you had 60k before and now you have 70k... I'm sorry but your line of thought makes no sense at all to me. I'd be fine with it.
Except that happens all the time, you just don't know about it. This is what its all about - transparency and disclosure. If you keep the first guy in the dark (as 98% of corporations do), he doesn't feel "bad" enough to get out and you trim some cash on both.
The argument usually goes that some people deserve to be paid more than others based on more specialized skills, more experience, etc. That it's unfair to be paid the same as someone who's doing a more entry-level position than yourself.
This is not my argument, but it's what I've been told when I've had this discussion before.