The problem is that it's not uncommon for a dev/designer/etc. to not understand some of the reasoning for why a PM is requesting changes be made. We all snicker at the incompetent PM who just wants to "make their mark" on a project, but very often the demand that may appear that way is motivated by entirely legitimate concerns. (And yes, the PM should bring the dev along with them, etc.) If you "add a duck" and the PM ends up missing the legitimate concerns as a result, everyone loses.

The add-a-duck attitude fundamentally assumes that the dev/designer knows what's best for the end product and the customer, and while that happens some of the time, the reason the PM role exists in the first place is because that's not always true. :)