They're scary because it's very easy to imagine a world where they win. The border policies of the EU wouldn't even have to be expanded/changed that much for the ecofash to get what they want, and their rhetoric is akin to what an actual "national socialism" would be sold as, "oh no we need to redistribute for our people, not those dirty browns in the global south, those we gotta keep out so they don't come and take our wealth (which we totally didn't rob them of)"