seems like you've started with a hypothesis that you might want to challenge. I have little knowledge or interest in the subject, the whole left and right thing is nonsense, just different ideas that should not be subject to binary categories. but it took me 2 mins to found at least one paper examining fascism within left wing politics. Not to mention the obvious clue in the name Fascist Union of British Workers.
If you read that article it disagrees with you, when you consider the origins. Nobody is disputing what it is today. Perhaps the author is smoking something. Either way, his article is published for critical review.