The erasure of white (European) ethnic identity is part of a wider societal trend.
Casting choices for actors in works of fiction have NO power to erase "white ethnic identity." If they cast a black actor to play George Washington, it would not and could not erase the historical facts about George Washington. Your use of terms like "erasure" and "genocide" is highly hyperbolic and makes it difficult to converse with you in a reasonable manner because it creates the expectation that you will not accept or respond to reason.
There is likely some prejudice against white people from certain races, some of which is (let's face it) a justifiable response to how white people have historically treated their people, and some of it is not.
Each individual is fine. I like these actors, and I like these shows. But the trend of anti-white hate, is alarming.
Casting minority actors in roles that have been previously portrayed as white is neither anti-white, nor hate. In most instances, it's likely to be one of the following:
1) a commercial decision to try to appeal to a broader audience. Broadcasting outlets and film studios care about money and that's it. That's why the horrible Tansformers films keeps getting sequels: because people keep paying to see them.
2) a specific vision on the part of the artist who created it.
3) the minority actor was simply the best actor who auditioned.
Today, when whites are being pressured to become blacks, it is a symptom of a societal dysfunction.
Whites are not being pressured to "become blacks." Most of the African-Americans who I've known have preferred it when whites don't try to adopt their culture.
When each European ethnicity is made unable to preserve its own unique cultural heritage and borders, it is a symptom of a societal dysfunction.
Are you actually saying that your cultural heritage hinges on the race of actors and actresses in works of fiction created by the entertainment industry?
Also, yank Cap, Johnny, and any other product of the "melting pot" off your list when you're talking about preserving "unique European ethnicities." Most Americans truly don't care about preserving their ethnic heritage. Most Americans who find out they are Irish might switch to Guiness or plan to take a vacation in Ireland, but only the rarest handful are actually going to attempt to learn Gaelic (much less follow through on it) or keep abreast of Irish politics or learn how the Irish government works.
More urgently, when European ethnicities are forbidden to defend against - or even criticize - Islamist jihadi ideologies, it is a symptom of a societal dysfunction.
Last I knew, criticizing terrorist ideologies is not frowned upon in the west, unless one is conflating Islam with terrorism. Terrorists have used and abused various ideologies over the years. Christian terrorists have blown up or shot up abortion clinics. Racial supremacist terrorists have blown up and burned down churches and synagogues. Mormon terrorists raided people in the frontier. Irish political terrorists have blown up, well, just about everything at one time or another. And so on.