If you want to talk about the egos of members and disruption of their play and some of the other cost things mentioned that's fine but it only relates to the egos of members and the disruption of their play and those other cost things mentioned.
But if you want to talk about the question of "adding bunkers later" in an architectural context alone that's another thing. Maybe adding bunkers later isn't even practical at public or even some private facilities but again that's not much of a strict architectural answer.
For a strict architectural answer to this question it might be good to analyze exactly what William Flynn meant to say when he recommended this exact technique!
And to go on and say that to do such a thing as adding bunkers later is completely unacceptable would be to say that Flynn, William Fownes (Oakmont) and Herbert Leeds (Myopia) were complete idiots! It would also say that even Donald Ross was wrong when he came back to my course ten years after opening and recommended the addition of a few bunkers.
As far as what kind of message that sends to memberships and green committees about adding bunkers on their own--that's a pretty simple answer too. Point to Ross and many of the others when they said (in writing) that the best policy is to depend for such things on your architect!