"It's wrong to resent a child for the sins of his father"
Whitebeard
"A child who is yet to be born bears no sin"
Gol D Roger
Now we got hiyori teaching kozuki propaganda and making it seem like all the kurozumi are evil.
What about kanjuros parents
This completely contradicts earlier themes of one piece
Dude, it is not going against One piece themes. It is an ideology of people. One piece represents many themes and the main theme is freedom.
There is no comparison between Hiyori "who is living in the closed island' and Roger 'who has seen the world.'
This is not the first time we have seen generalization in one piece.
1) Luffy said he hates celestal dragons when he has problem with only one.
2) Sanji asked Jinbei to kill himself when Arlong was the one who caused damage to Nami.
Fisher men hated humans and humans hated fishermen. Nami didn't change her opinion until the Saboady archipelago. Nami has seen the other side here.
At the same time, Akainu represents good people but he follows 'all pirates are evil'. If you look at it, there is no difference between Akainu and Hiyori. So, why didn't you have the same question around that time?
People don't change easily until they see the other side. Hiyori didn't see the tragedy of kurozumi and also didn't meet good kurozumi for her to change her mind. Mind you Wano is still closed borders. So it is realistic that Hiyori had the hatred towards the whole clan. It does no way represent One piece 'theme'. If this represents the whole one piece 'themes', then most of characters thoughts are counted as themes that contradict one piece.