Well, they can take away religious approval; but it’s a lot harder to take away culture, ethnicity and DNA.
I know Jews who aren’t religiously observant, and some who are atheists; but they all call themselves ‘Jews’.
(By the way - how many Jews do you know who have converted to Christianity?)
Personally? None. I wish there were more.
Thirty years ago, I did meet a Jewish woman who believed in Jesus. But she did not consider herself a Christian. She called herself a "completed Jew."
She was an aspiring actress, a friendly, mellow hippie sort (she'd be in her 60s now). She told me she had been a drug addict, then found Jesus, and that Jesus had cured her addiction. So she believed that Jesus was the messiah.
But she still considered herself Jewish.
So I told her about Messianic Judaism. She was shocked. She didn't know there were others who considered themselves Jewish yet believed in Jesus. She thought she was the only one. She came up with the term "completed Jew" by herself.
I don't know what became of her.