There is a more pernicious vibe that has been eating me: People who claim that a teacher who doesn't charge a fee to students is somehow superior to those who do charge.
In Europe this idea is historically inseparable from hatred of Jews. A Jew, by definition, lacked virtue. The European definition of a noble gentleman was of course predicated first on being born to a father and mother of noble birth. But that title could be revoked if you failed to protect the honor of your women or your name. Opening a store or pedaling goods was a quick way to lose your nobility.
The word luxury has come to mean something nice that isn't cheap, but it used to be a sin. To commit the sin of luxury was to have objects or products and services that were reserved for people of a higher class.
Offering a service for free meant you were avoiding the taint of money. Aristocrats controlled everything, land, church, food. Aristocrats did not concern themselves with money, that was the way of peasants and merchants who coveted the luxuries of a life they were excluded from at birth.
In the Middle-east, prices are still set by complex family tribal relationships, anyone outside of that system lacks virtue, and automatically gets a higher price. To offer services for free in this context would simply mean that you are accumulating social obligations in a society where those obligations trump money.
China was somewhere in between. A system of merit existed by which individuals could take an exam and gain a rank in the government or the army. People were also promoted within this system on the basis of their competence. Of course there was nepotism and corruption, but the basic idea was to promote a person because he was the best person for the job.
This existed simultaneously with big family networks. Chinese power can be viewed as multiple overlapping and concentric rings of family influence, each of which makes alliances with other circles of power, the government simply being the biggest most powerful family.
I'm not exactly sure why a certain strain of traditional Chinese thought has felt merchants, and itinerant performers were people of lower virtue. Perhaps it is an extension of the Confucian precept against calculating your advantage over others? More likely it is just a fear of people who are more worldly, people who have a drive to seek their fortune outside of the often stifling confines of village life.
Now add to this that the Communists made a totalitarian state religion out of hating independent business people. After all, business people travel and have a way of undermining the status quo by creating alternate sources of authority.
Doctors in Communist China in the 1980's had to see everyone for free. Gordon Xu (George Xu's brother) worked in a Hospital. He would arrive at 8 am and wasn't allowed to leave until everyone waiting in line had been seen. Most days that was after 8 pm, about 80 patients a day. The state paid him a small salary for his service.
There is no virtue in not charging a fee. If you want to reward low income students who demonstrate merit by giving them free lessons, that's great. But that's because you want to have great students, not because you are doing some great deed for society. Not charging money is often a way of creating social obligation, which has its own value. If you are already rich and don't charge, so what, it means nothing. If you are low income yourself and you don't charge, so what, it just means you don't need the money.
If honor and virtue are diminished by charging money, then they are things not worth having.