That is not true. Slaves in the Antiquity were personal possessions that could be sold, physically abused and even killed by their owners if they wanted to. Their condition wasn't like slaves in 19th century USA, it was worse. At least Americans didn't sacrifice hundreds of thousands of slaves annually for their entertainment like the Romans.
You could not have chosen a worse analogy than the modern Gastarbeiters. Ancient slaves, when they were lucky to work for a kind and humane family, were more like servants of upper and upper-middle class European families until the early 20th century, living with them 24h, and doing house chores, cooking, or taking care of their masters' children. Like house servants they got food and accommodation in exchange for their work, but had very little free time and usually (there were exceptions in both cases) couldn't marry or have children of their own while in service. The main difference was that modern house servants were not owned by their masters, could resign or change job whenever they wanted, and could own personal belongings, whereas slaves had to wait to be emancipated, which was by no way guaranteed and only relied on the good graces of their masters.
Nope there are 5 words with different meaning,
1 ΔΟΥΛΟΣ worker, they had everything except land and Vote rights,
Not allowed to fight, they were protected by master, the take 66%% of what they earned,
they were a class, a working class only, when they were free they earn rights,
the first corrupted Banker in ancient Athens was a δουλος that was set free and they him control of Athens central Bank
mostly farmers, merchants, and keep some things like fire, food stocks, also αχθοφοροι (carry things,)
the word 'work' in modern Greece is δουλεια, meaning how important they were to ancient society, and how their masters took good care for them
2 ειλωτας farmer, they had almost all the land in ancient Sparta, except the field of 4 000 m2 that was about to given to retired Ομοιοι, they give according land a % of production to omoioi, they did not vote, they did not go to war, about 15%
3 Συντεχνοι they are not mentioned widely cause some put them in class of δουλοι,
they were mostly metalsmiths, or builders, they support army as diggers sharp weapons, etc
But not allowed to fight
4 Δεκανοι helpers, mostly they help priest, ephoroi etc, they knew writing and they were payed
modern is the priest διακος a small degree in church degrees
5 Σκλαβοι, first mention by Xenophon in Κυρου αναβασις, (the cyrus attempt)
he describes that some rich man took people, they feed them and had them in cages,
the words σκλαβος means εις κλωβο, in cage,
so the type of slave who lives in cages and has chains was unknown to ancient Greeks, in fact if we read Xenophon he is astonished by what he seen,
the slaves in ancient Greeks is like modern workers Tax payers,
according city state they had priviledge, rights and obligations, as modern day workers,
they earn money, but gave tax to master,
THEY NEVER WENT TO WAR, except the LAST BATTLE, IN ACHAIA PELOPONESE.
another class was the semi free states like Arcadians to Spartans, Arcadians were semi free, they could go to war, to produce what ever, but they should use Sparta prices on Market, and only Sparta harbor,
THEY DID HAVE THE RIGHT TO VOTE,
a δουλος could be a master after his price was paid,
an ειλωτας never, except if he moved to another town,
In Makedonia we find similar system, the masters village,
Makedonians have democracy and absolute together,
they have democracy in city rulers, and market rulers, and protection rulers, only in cities and villages of συντεχνοι,
the rest area belong to military families, so a city with walls had democracy, but the military who protect did not,
out side city land belong to some military officers or the king, a village of farmers that lived there should produce only farming and warriors, all paid money, but did have the right to own land, only city people had small land, and the big military families,
the later sclavoi as is described in roman times, is half a myth,
besides Greeks were not saint, but they fear more the gods, than Romans who became gods,
the christian expansion also put some myths and exagerations in working class in ancient world,
a slave according time is something that always existed,
today we name them workers!!!
about same was in ancient world, except times when man became God,
at least until phillip's time we know that was a shame to have sexual with your slave,
in fact it was honor to have sex with 'captured' high class,
In Homer we see the 2 big fight about 1 girls,
it was an Honor to have a captured one of high class, even to marry one,
it was not honor to have a slave for sex, at least until phillips times,
Αισωπος was a doulos class teacher, who become free and still worked as teacher, did not changing class,
we have many cases of friendship among the 2 class,
the later roman gladiators, and sclaves and etc is another story,
remember the first brothel was in middle East, and still sclaves were like working class,
the inhuman face to a sclave is first written in Xenophon, and later and became giving gifts sclaves in west world, a pair of blondes, or a strong Numidian worker, or a educated Greek,
it is another story the paid doulos, and another the free work sclavos of later,
In fact I believe sometimes that was better,
the modern case that a human will work a whole life in Corporation that belongs to Mr Z and paid, and when war comes, he will go to fight to protect Mr Z property while Mr Z will not go to fight, as in WW2 europe was, I believe is more unfair,
Besides in ancient world, at least Greece, sclaves lived in his Mastrers house, or had their own houses,
today modern Slave merchant bring people, in a pathetic boat, to pass Aegean or Mediterrenean or Adriatic, they take money from slaves thousands of E per Head to pass them from Pakistan to Eu, and they abandon them where ever, full of disease, hungry and uneducated, the use them in as cheap workers and they let them live in inhuman conditions,
at least in some eras and areas slavery was better than today,
just think, some people today pay to become slaves !!!!!