In the Dialogues(specifically The Republic), when he is discussing his Utopia, At one point, he does say that children should not be treated differently based on their parent's status in life. However, I did not see any mention of slavery in this discussion, so I want to know what did he propose about the practice of slavery in his Utopia? Also, what were his views of Slavery in general?
There is no special cast called "slaves" in Platos Utopia. Instead all children are given to the state to be brought up and given work as the state sees fit once adult. Hence, almost everybody are slaves. ref Although all people are "citizens" these "citizens" have no rights, only obligations, and no freedom at all except for the absolute upper part that rules the city.
Plato wishes to abolish freedom, and hence in our terminology make everybody slaves. He tries to cover this by claiming that rulers are enslaved (by responsibility and fear of those who rules over) and in pure NewSpeak claim that freedom leads to slavery. (ref: The Republic)
In Platos later 'Laws', he describes another city which he thinks is more realistic, and it does have a separate slave cast. ref
Platos view of slavery was therefore quite clearly very positive. But he knew that the word was negative, and therefore tried both to associate things he did not like, primarily freedom, with the word slavery, and also tried to excuse tyrannic rulers by claiming they actually were slaves to the people. But people that we today would call slaves, are people he wanted many of in his ideal states.
A knife is good, he said, when it cuts efficiently, that is, when it fulfills its function.
The assignment of all people to their respective classes would come only after extensive training and only those capable of doing so would progress to the higher levels. Although theoretically all people would have the opportunity to reach the highest level, they would stop in fact the level of their natural aptitudes.
This implied that by nature some would be rulers and others craftspeople, and would provide the basis for a perfectly stratified society. Whereas later societies in Europe assumed that children born into such a stratified society would stay at the level at which they were born, Plato recognized that children would not always have the same quality as their parents. He said, therefore, that among the injunctions laid by heaven upon the rulers there is none that needs to be so carefully watched as the mixture of metals in the souls of children.
If a child of their own is born with an alloy of iron or brass, they must, without the smallest pity, assign him the station proper to his nature and thrust him out among the farmers and craftspeople. Similarly, if a child with gold or silver is born to craftspeople “they will promote him according to his value.”
Most importantly, Plato thought that everyone should agree on who is to be the ruler and agree also on why the ruler should be obeyed.
First of all Plato's Republic which you mention as Utopia has many parts taken from existing cities and legislations specifically Sparta and Crete.
Concerning your comment on slavery. Broadly speaking Plato belonged to the Athenian Aristocracy. He believed, and is evident in the Republic that not all men are created equal. In the Republic, there is no explicit mention of slaves per se but, men are separated in 3 distinct divisions depending on their personal merits.
One thing to note here, since the concept of slavery in Greece has been misinterpreted by a lot, is this:
- The king in Plato's Republic is the absolute best. The best in all aspects. The best warrior, the best philosopher the most capable person by any standard.
- There are no hereditary rights to powers. I.e. the children of the division of the warriors do not necessarily stay in that division. If they are not fit to be warriors, they might fall into the division of farmers.
So to answer your question, division 3 is the division that is somehow the slaves of Republic since all they do in life is work to feed themselves (and families) of course but to feed the other 2 divisions (the republic's elite) as well.
This is not far from what slaves did in Ancient Greece since their treatment was not as you imagine or happened in Egypt or elsewhere.
Also note on this that slave in Greece is δοῦλος which is the root of today's word for work in Greek.