Has this happened to anyone else?

A couple of times in my life (one was decades ago, and the other was just a year or two ago), I have run into people who literally believed that Jews drink blood on Jewish holidays. When I pointed out that this isn’t so, in both cases, I was told that I had no right to challenge the statement EVEN IF I have any proof or experience showing that it wasn’t actually true, because the statement was part of the cultural/religious beliefs of the community that the statement-maker belonged to or Head grown up in. Basically: “it’s just part of legends and beliefs, where I grew up, as part of our culture, and nobody has any right to take that away from us by finding proof otherwise. Your statements that it isn’t true, cannot stand up against my live experience that this is part of a story in my culture.“ Has this happened to anyone else? If so, what did you say and do?