Opposition is Zionism and opposition to Israel's treatment of Palestinians is not the same thing as antisemitism, and I think you are deliberately conflating these issues as a smear to leftist causes.
The guy who killed Jo Cox, Thomas Mair, was heard yelling "Britain First" as he attacked her. He had attended white supremacist rallies before then. Yes, he had a history of mental illness, but extreme right-wing leanings and mental illness historically have an awful lot of overlap in a venn diagram.
I don't know who taught you history or what papers you read, but calling fascism a product of the left is crazy town. Soviet 'fascism'? Someone should have told Hitler that before he invaded the USSR, it would have saved him an awful lot of trouble. I am not going to try to explain to you what constitutes Fascism or what its ideological roots are, there are plenty of good resources for that, and if I pointed you to them, I have no doubt you would wave them away as liberal propaganda. And no, there are not plenty of others who adhere to the view that Fascism is a product of the Left, even in conservative circles. You might be able to cite an editorial written by a hard-right kook, but I would cite every single credible scholar on the matter; historians, sociologists, political scientists- any serious person who has ever had to study the subject.