Was there anyone in ancient Rome who thought that the class structure was unethical? Or in 14th century France who thought that the monarchy and the church shouldn't have so much money while there were people starving?
And if 19th century socialists were the first, where did they get their ideas? Who influenced them?
More of a follow-up question than an answer...
How accurate is the following quote attributed to the priest John Ball at the time of the English peasants revolt? Because it certainly sounds rather modern:
"When Adam dalf, and Eve span, who was thanne a gentilman? From the beginning all men were created equal by nature, and that servitude had been introduced by the unjust and evil oppression of men, against the will of God, who, if it had pleased Him to create serfs, surely in the beginning of the world would have appointed who should be a serf and who a lord".