I have based my opposition to P4P in medicine on several lines of argument. These included :
1) It is unethical (see here for the comments of Drs. Edmund Blum and Faith Fitzgerald)
2 ) it often is a disingenuous method to control costs with feigning a desire to improve care
3)Goodhart's Law (see here).
Now the prolific Dr. Doug Perednia offers another reason to oppose P4P. Read about it here ( this is part 2, read Part 1 also). He offers a brief and very instructive introduction to a field of study known as Self-determination Theory (SDT) and relates that to the P4P issue.
SDT is based upon the idea that there are many things that people do not for the promise of external reward, but because of some sort of intrinsic, human desire for autonomy, competence and relatedness.
Including in that category of things people do not necessarily because of carrots and sticks is the practice of medicine.
The theoretical and empirical case against P4P has grown so strong that the only reason physicians and their organizations put up with it must be they just want to go along to get along.