I'm French, English, Scottish, Welsh, Dutch, Irish, Italian, Spanish and a touch of American Indian. No big deal, I'm a mutt.
My son is almost 3, VERY smart, VERY verbal. He has infrequent supervised visitations with his father. After a recent visitation, my son came back and casually mentioned how Greek is good, not-Greek is not good. When race and culture and ethnicity comes up with my son, I just give the facts- Mom-Mom's this, his father's that, he's both, etc. My son's father is 100% Greek and proud of it. In fact, he goes way beyond "I'm Greek and I'm proud"- he's made comments about me about how it's a shame our son is "only" half Greek, and how he's got such a proud heritage and my side of the family" doesn't even know what we are", etc, and how everything needs to be Greek, Greek, Greek, and if our son doesn't fully embrace his Greek side and forget his other side, then he'll pretty much be disowned. My son's father has some very scary mindsets along the line that Greek is the only pure race. In other words, father's side- Greek- is better, Mom's side- a little of a lot- is something to hide, something to be ashamed of. I expect this... I don't know what to call it... indoctration?... to only get worse as my son gets older. I don't want my son to grow up either thinking he's better than everyone because he's Greek, or thinking he's not good enough, because he's only half Greek.
How do I successfully help my son to learn that ALL his sides are good and acceptable and that his father's side- Greek- is not the only good side?
Have you discussed your concerns with your son's father?
Other than that, I would just kind of downplay it - say "Yes, Greek culture is great - but lots of other cultures have contributed a lot too. There is good and bad in all cultures and rather than focus pride or shame on what our relatives do or have done, think about how you can contribute to the world yourself..."
I'd show respect for your son's father's beliefs while also making it clear you don't agree, even without the courts involved, it will probably be less confusing for your son and will also help him with accepting people of different religious beliefs and such- which is also important. Teach your son cultural diversity and show him that he can be proud of his heritage without thinking it's better or purer than others'. I would support him being proud of being Greek, and show him how to be proud while still appreciating all cultures, and also show that you're proud of your own heritage and let him know it's okay to be proud of ALL his heritage.
I'd also teach him to be careful what he says around other people and kids. You can't force him to stop believing what his father's telling him, only help him see other options, but he'll have a really hard time making friends and could even get in trouble if he starts saying he's better than other people based on his race or that his culture is better than theirs. Let him know he can talk about this with his father and say it around only you, but it's not something to talk about with other people.
Because the court systems are so ridiculous- could you get in trouble for going against him on this, like, if he disowns his son over this could he "blame" you for teaching your son to "go against him" or some crap? I really hope not, but there's a lot of things I'd hope wouldn't happen that the courts do. :( This is the man who only has supervised visitation with the boy, right? Apparently the system thinks his views are acceptable enough that either the person who supervises the visits doesn't have a problem with it or can't do anything to stop it, which is why I'd be concerned.