I felt exactly the same way. People who probably didn't know I am Jewish because it never came up in conversation (I live somewhere there aren't many Jews at all, so it doesn't really occur to people that there may be a Jew among them) but with whom I had built lovely friendships. Nevertheless, I didn't feel that this lack of knowledge of my being a Jew in any way excused them of their antisemitic/Israel-demonising attitudes.