If so, you are wrong.
When most Americans think of "fascism," they think of Mussolini. The dictionary.com definition of fascism is this: "a governmental system led by a dictator having complete power, forcibly suppressing opposition and criticism, regimenting all industry, commerce, etc., and emphasizing an aggressive nationalism and often racism."
Antifa doesn't actually oppose that, as long as they are in charge.
Read up on antifa (antifaschistische aktion). They have been around for 100 years. If you only just heard of them in the past few years, I can understand why you might think they oppose fascism. They actually oppose capitalism. They believe an unhealthy dictatorship is the natural result of mature capitalism, so they oppose capitalism. They seek to impose a benevolent authority along the lines of communism.
Antifa does not oppose "fascism" as you or I were taught about it in school. You need to read these websites with their meanings in mind, not your own. Otherwise, you will miss what they are actually saying. They have their own language of sorts...all specialists do in their area of specialty.