but if the principle is that I have to pay you what other people are making, then perhaps I just can't hire you to begin with. Some people would say that maybe I should not hire you if I can't pay you the same as someone else. I don't know if I agree, but I can see that argument. Still, I'm out a worker that I could really use to unburden everyone else on the team.
If you are willing to work for 80K, I am happy to give you bigger merit raises than your peers if you worked extra hard, but if you walk in the door unhappy with your base salary, should I cut into the bonus pool of others just so you can get a massive raise to make your salary equal to theirs? Didn't they deserve their raise too? Or do they deserve less simply because their base number is higher than yours?
If you know that a certain role and experience level in the company is being paid $X then you know out of the gate that if you are going to try to find someone for that same role for $X-20% that the person you find is being underpaid by your own company's standard. If your existing employees at $X are making close to market rate then you know that this new employee is being underpaid by the market's standard.
I agree with you that just because you can't pay them that $X rate doesn't mean you don't hire them--If you have someone who is willing to accept the position and is a good fit then of course go for it! However you need to recognize that this person is being under compensated by your own standard, there is a possibility that due to job market they may in fact not be happy out of the gate with that salary and may have accepted it under the expectation of faster salary increases in the coming years.
As the employer you need to recognize that you're receiving an extraordinary value from an employee who is/was willing to work for less compensation than other similar employees. One of the things you have to deal with is that the employee may easily recognize they are under compensated; If that employee wants more compensation you need to make a choice: Either you improve their compensation until they are satisfied or you may have either an unhappy worker or possibly a new vacancy that you have to fill with a budget that represents under compensation.
Now consider this: Were your existing employees being better compensated because they were previously overworked which is now resolved with the new hire? What situation will you be in if this under compensated employee leaves because they find better compensation elsewhere? You'll have a team that is down a person, probably now feeling even more overworked than before because they've just taken on parts of someone else's role, but most likely with no compensation adjustment.
So to answer your question of whether well compensated employees should receive less in order to bring up a poorly compensated employee the answer in my opinion is YES, if you want to keep a healthy eco system in your office.
I'm a proponent of giving raises based on dollars vs. percentage. It provides a path to better equitability of pay while staying "fair" in a "what did you get?" style measurement contest. In that regard you've just given two people an equal raise, so the person with higher compensation and the person with lower compensation are receiving the same thing. If the person with higher compensation wants to complain they have to be prepared for their base pay to stand up to the light of comparison to the person with lower base pay. If they are truly even employees then the comparison will fall in favor of the person with the lower base pay.
What I don't think is that you should consider what someone else makes to be a reflection on what the company thinks of *you*. If you're capable, you may start lower, but I'd probably be happy to see you become a manager or advanced individual contributor where that other guy will never get higher than he is today. You'll start at 80K, but you'll someday get to 150K whereas the other guy will never see the other side of 110. Alternately, you could be selected for more training opportunities or given more interesting work. All of that turns into more money too, either at that work place or at another place you move to later.
What a company pays you represents your value to them (what htey think of you) in the most obvious way. If you and someone else are doing the same job you should be relatively evenly compensated for the job unless you're working somewhere that increases pay based on seniority. So in that regard it's very difficult to tell someone that the guy who does the same job you do, but is paid 30% more, doesn't reflect on what the company thinks of you.
In my opinion that company thinks you're a chump and they're going to continue to pay you less until you force the situation, which is only going to create animosity. It's much better for the work place eco system if, over time, employees of the same role are paid relatively equal salaries which are tied to market values for those roles.
To be honest I almost thought you were being satirical with this last part when you say that as a "capable" employee (does that infer to the other is not capable?) I'll have more opportunities than the other employee who may be making more than me today. What a bunch of textbook HR/manager horseshit :) "Just keep working hard, paying your dues and it'll pay off! You'll see!"... to re-use your earlier arguments regarding otherwise equal workers: Doesn't that other worker deserve the advancements and more interesting work too? Is it really fair that I receive more advancement and interesting work than another person simply because my base is lower than theirs? So even if I am a "capable" employee, what if the others are too? Aren't we back to the same problem?
I also won't go down the rat hole of how certain types of managers will specifically NOT spontaneously advance employees who excel within a certain role because it means they are losing an excellent employee in a position they know they will have a hard time replacing. Either you end up with an employee who advocates for themselves or one who is too meek and potentially winds up feeling under appreciated toiling in anonymity.