Even ancient Romans knew that quid pro quo corrupted both individuals and society.
Quid pro quo was a really in social, economic, and religious structures.
Socially and politically, it was caught up in the patronage system, the structure of pyramid hierarchy that bound people in classes of benefactors and beneficiaries with legal obligations of provision and loyalty.
Economically, it was the targeted use of wealth or gifts by a benefactor to achieve some end. Romans didn't believe in freely-entered contractual lending. They believed in using cash to BIND lesser status people into relationships of duty. 
Although this was just a part of the (deeply unjust) economic system, it was easily corrupted wherein benefactors became richer and beneficiaries pushed into debt.
And that debt could result in imprisonment, exile, slavery, or execution.
And that debt could result in imprisonment, exile, slavery, or execution.
Quid pro quo was "normal" Roman practice (one Jesus criticizes in Luke 14). But it undermined Roman society, created terrible inequities, and a corrupted the ruling class.
It was also a religious practice, whereby the gods offered worshippers some desired end in return for worship and tithes.
It was a system of divine bargaining.
It was a system of divine bargaining.
All three senses -- social hierarchy, economic corruption, and religious bargaining -- continued in western culture long after the fall of Rome, influencing (especially) medieval feudalism.
A constant undertow of criticism in the Reformation and the Enlightenment attacked quid pro quo. Some of the most influential thinkers in European history recognized the dangers of such -- they argued quid pro quo was the enemy of genuine freedom, equality, and morality.
This includes all the most important "dead white guys" of Europe -- folks like Martin Luther, John Locke, Adam Smith.
The same thread of argument is found in writings by European women - writers like Jane Austen, George Eliot (yes, she's a she), and early feminists like Margaret Fell and Mary Wollstonecraft.
Quid pro quo was a foundation of the southern enslavement hierarchy, in all three dimensions. White slaveholders considered themselves "benefactors" of those they enslaved, whom they believed "beneficiaries" of their economic, social, & religious largess.
So, much political and religious thought in African-American culture developed as a direct attack on quid pro quo-based structures.
The "benefactor" take on slave holding is most obvious in white sermon literature from the 1830-50s; the rejection of it is an important strand of Frederick Douglass' work.
Historically, quid pro quo is the long shadow of social, economic, and religious inequality that has fueled many of the worst aspects of western culture.
Both the smartest western thinkers and those oppressed by quid pro quo have known this for the last 2000 years.
Both the smartest western thinkers and those oppressed by quid pro quo have known this for the last 2000 years.
That's why free societies, why societies even striving for such, have made quid pro quo (in many instances) a crime (esp for public officials and business leaders) and morally repugnant.
Please forgive typos, etc. I noticed a few above. My threads are always extemporaneous - and sometimes my enthusiasm exceeds the talents of my typing.
And, in case you were wondering, the opposite of "quid pro quo" is "pro bono," meaning "for the good, for free." I don't know about you, but I'd much rather live in a pro bono world than a quid pro quo one!
