Damoshe, merely meeting antisemites isn’t the issue – rav yosef chaim zonnenfeld sent yaakov dehaan hy”d to do that too…rabban yochanan Ben zakkai pleaded with Vespasian for mercy; this has a lot of precedent.
The issue is what they’re saying at those meetings. If all they did was say to have mercy on the Jews living in Israel because a great number aren’t zionists, that would have been fine. What they do is, seemingly, condone the violence and show support for Iran’s genocidal goal, because they think they must do so in order to get rid of the state by any means necessary.
And that’s what they do when they march with the genocidal “from the river…” people.
It needs to be stressed that this is a very, very small number of people. Neturei karta are mostly Yerushalmis in meah shaarim who would never engage in these activities. It’s a rag tag group of mostly baalei teshuva who were led down this road. There’s only about 50 of them in the world, but they have a large media presence.
Their founder was a big tzadik, rav amram blau, who was known in Yerushalayim to take in the most disturbed, poor people who no one wanted to have a shaychus with. He’d give them fresh clothes and a hot meal.
A kanoi leshem shomayim can be identified by how he treats people and if he gets angry at other, non leshem shomayim things. Rav amram was a very big tzadik who loved Hashem, and couldn’t stand the pollution of eretz yisroel with tumah. But he’d never endanger even one Jewish life to achieve his goals.