We can analyze Fascism, summarize its general aspects, and apply the definition to other movements. Hence why we can call Nazism fascism, even though they were separate parties. Trumpism is fascist. This is the point the article is making, and it has been made thoroughly elsewhere as well. At this point, it's is just basic table stakes discussion context for anybody who loves individual liberty or believes in the Constitution and limited government. If you're still unable to even entertain the idea, then you're part of the problem. Based on your touchstone strawmen of "leftists", "radical", and "activists", it sounds like you've got a heavy case of TDS - the real TDS, not the accusation-in-a-mirror version.