Well, when I was young, even before becoming interested in Judaism, I realised that there is a lot of anti-Semirism here, and I classified it in four possible situations.
1- If someones hates the Jews for what they really are (that is that persons hates Judaism or Jewish life style or traditions) then he is infected by the anti-Semite virus, and I don't waste my time in him.
2- If someone doesn't really hate, but dislikes Jews for what they are, then he is also infected, thoush less dangeroous. Why explaining him?
3- If someone believes in or makes conspiracy theories AND hates Jews for that, even if he really believes sioncerely in that theories, then he is also infected, since an honest person should seek better information before hating!
4- If someone simply believes in conspiracy theories he heard from others (out of true ignorance), but there is no hate involved, then I try to explain him that he's wrong