QFT
There is something inherently prejudicial about any show of ethnic pride. Now if you want to have a "heritage day" where you celebrate the ethnic heritage of a group that is a positive outlook on ethnic appreciation, but T-shirts that say "blank" pride are devisive without any of the heritage involved.
For example, I work with several african born physicians, my roommate in med school was from Haiti and my next door neighbor's ancestors were victims of slavery. These people were very different. I would go as far to say that it was only the prejudice of others that created a common experience for them.
I was watching some old footage of germany pre-WWII and I saw all kinds of "pride" statements, and other signs of nationalism. I found it disturbing, especially knowing what happened afterwards.
Maybe it has something to do with a bit of multicultural background in my family, that I feel uneasy with too much nationalism. Although in todays world, a mix of German, Irish, English, French, Italian and Croatian, doesnt seem like diversity, it was enough to highlight the divisive nature of nationalism.