Do you have a reference for this? I've honestly never heard of this and had no idea, even though I study politics and economics somewhat closely. I've never seen this brought up as a point on either side when talking about taxes, so I'm curoious if this is the case if there are exceptions that have become the rule and thus this might be technically true but not seen by most people?
A progressive income tax like this prevents situations where someone getting a small raise that moves them I i a higher tax bracket could actually leave them WORSE OFF than they were before the raise.
It's how tax brackets work. Notice the "+X% over the excess / of the amount over" wording in the documents. I'm not a CPA, so maybe one can chime in with a counter example of someone who would take home less if they made a larger salary. But I'm pretty certain this is how it works.
TL;DR: taxes are hard, do you have a reference?