Oh, they do. They hate others because they hate themselves, and they were taught to hate themselves since before they were born.
Like with the Irish you mentioned in New York, every immigrant wave that comes to New York goes through the same thing. The Irish were picked on by the English and the Germans, then the Irish picked on the Italians when they came here. Then the Italians picked on the Puerto Ricans and the Blacks that came after them. Now the Puerto Ricans pick on Dominicans and Mexicans while the Blacks pick on Koreans and Haitians. Of course they're picking on Indians and middle Easterners as well.
And that's the thing of it, they don't hate the ones who picked on them, they hate the ones who came after that are going through the same thing that their parents went through. It never made sense to me.
When my family moved to this neighborhood in the 1970s, I was picked on because my mother is from Puerto Rico. I resented the Italians for what they did, not the Dominicans. I did realize when I got older that despite a lot of talk that they do, Italians are not as bad as some other people might be. Sure, some called me names, but if we lived in an Irish neighborhood, I would have been getting beat up in the bathroom at school by half the class on a fairly regular basis.
Even when you explain to people the hypocrisy and the irony, like I have with a sibling on more than one occasion, they don't get it. We have talked about this very subjec. Prejudices wrong. Racism is wrong. Hating people just because of the ancestry is wrong. Except for Dominicans, she believes it's justified for Dominicans, they are the exception to her. When I try explaining how ridiculous that sounds, how hypocritical, nope, she said it's justified in their case. They are the exception that proves the rule.
But like I tell her and other Puerto Ricans that say the same thing, you know what the difference between a Puerto Rican and a Dominican is? A hundred miles. That's it, a distance of a hundred miles. Our cultures are more similar to each other than they are to other Hispanic cultures, except Dominicans, being from a bigger island with more people, have better variations on foods than we do. That's it. We got one or two versions of this, they got 10 of the same thing.
Humans make me laugh.