You mean the irony is people whose language became popular are salty about having immigrants corrupting their culture? That's a stretch of the word irony - it's like saying it's ironic that a successful athlete is unhappy about losing a competition because his previous success came about from other people losing. People who are competing do like to win and don't like to lose. That's completely normal non-ironic thinking.
> doesn't mean I have contempt for any group of people.
Describing their behavior as whinging and putting "their culture" in quotes shows contempt. I'll show you with the NZ Maori example. See if it looks contemptuous:
I find it ironic that vocal factions of the New Zealand Maori population are whinging about "their culture" being sullied by immigrants.