This is the passage that sticks out to me when I am reading Vicentino's 1555 Ancient Music Adapted to Modern Practice and shortly after teaching 20th century music:

"All the same, I notice that nowadays some singers and musicians, who believe themselves knowledgeable, show their amazement to everyone whenever they encounter a novelty in musical signs that has been introduced for the sake of some sort of consonance.  Straightway they begin by saying, 'It is not good, it is not easy to sing,' and conclude that 'it will not endure,' citing the example of past composers to prove that if the practice in question were good those composers would have used it.  Thus do these singers and musicians betray to all that they have forgotten how to study their profession."
(Maniates translation, 37)