The reason is obvious. Chilonim are for the most part tinokos shenishbu. They didn’t have a good experience or any experience with Torah. They are less responsible because it is the situation that they were put into. In fact, it’s probably more our fault then theirs for not succesfully bringing them closer to G-d.
But Neturei Karta should know better. They are frum in most respects and yet still act the way they do. and in the name of the Torah. They are the ultimate chilul Hashem and the fact that they are otherwise “frum” is not a redeeming factor. A person who is learned and is still mechalel Shabbos bemeizid is on a whole different level than one who is not frum at all. There is a higher standard for the frum, and they fall much farther when they don’t meet those standards.