I mean, Black Panther, I can understand as an African King. Luke Cage is a Black Man because a huge part of his identity is that he's a take-off of Blacksploitation cinema in the 1970s.
But what about Wally West is "white?"
I always liked Tanaka Rei/Flash from Marv Wolfman's Legends of the DCU issue because it was such a weird fit that worked for a character. Being someone who was Asian, I could identify with Tanaka Rei in a way that I know I didn't with Barry Allen.
Being Asian wasn't his defining characteristic. It was just a part of the character that made him seem more relatable because I knew Japanese-Americans like Tanaka Rei.
I don't mind blind ethicity casting when ethnicity is irrelevant to the character. It would make any sense to make Abraham Lincoln Black or Black Panther white because race and ethnicity define both characters in specific ways. I don't know why, but while I know Wally is a white guy, his "whiteness" is not definitive to his character.
To each his or her own, but I believe you lock yourself out of some great stuff if you only see it as a "white" or "ethnic other" part. In these long-running TV Shows, you end up losing out on great actors if you adhere strictly to the original intent of the comic book.
That he's a ginger. That's his defining characteristic.