but the article argues against creating the abstraction when the functionality was the same in both places, which I disagree with. To be honest, the whole topic

but the article argues against creating the abstraction when the functionality was the same in both places, which I disagree with. To be honest, the whole topic disregards whether the two pieces of functionality are actually doing the same thing in a domain-logic sense or simply a code sense, which is the heart of the issue. If the similarity is coincidental (e.g. validation on two model types temporarily happens to be the same) then the abstraction should not occur. If it is not (e.g. two distinct operations on a model type happen to have an identical subroutine) then the abstraction should occur.