You have to understand that some of the people spreading their “hate” posts are bigoted & ignorant. They love getting a rise out of you. They annoy me as well, but I know that by answering them, that they LOVE the confrontation. Think about it, why are they posting these comments on an online forum? because these people are afraid to do ANYTHING in person, they feel powerful when they are fighting with people in the safety of their home.
The sites themselves are not necessarily anti-semitic, they just hold by “freedom of speech” So people can go on there spewing just about anything, unless they get a few complaints about the comment, then they take it down.