Those who offer at most 10% increase when a person's value is 50% higher will find themselves missing the good employees and ultimately, failing.
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An example:
How much do I offer for this house? I have have no friggin' clue. But I can look at previous sale prices to get an rough idea. Naturally, I if trust my decision to that 100%, I'll risk making a poor decision. But the previous sales are a piece of information about the market that I ought not ignore.
I like the example, but wouldn't it be more parallel to ask "How much have you offered for other houses?" or "How much did your previous house sell for?". The seller would love to know that you are capable of offering more, but you are (properly?) reluctant to give this information.
> But the previous sales are a piece of information about the market that I ought not ignore.
I don't think there is any dispute that this is valuable information to the person doing the hiring. The question is whether it is fair to the person being hired to be asked this question.
Despite the theoretical disadvantage to the business, the current result seems to be that those who are historically disadvantaged will remain disadvantaged, while those who started out with an advantage will be disproportionally rewarded.
So those question would be more like "How much do you pay other employees?" or "How much have you offered other candidates?"
You can ask those questions. Some employers are upfront, even posting salary ranges in the job ad itself. Other employers will decline to share that information.
Either side can reveal as much or as little information about their employment history as they choose. Curtailing freedoms is a heavy-handed act, despite the theoretical advantage to candidates.