I don't think that most of the people on this site are fascists, either. They're just confused and scared.
People hate the Antifa because their actions come off to many as a violation of the American constitution. One of this country's main gimmicks is that you say whatever you want and express yourself however you want without being punished for doing so.
This idea sounds excellent on paper. But people tend to abuse the hell out of this law. Because of this, we have people who promote mass genocide, racism, and xenophobia be tolerated by society. I don't know about you, but this may lead to some horrible things happening. Do you want to risk xenophobic racists running this country? Neither do I. It'll be Nazi Germany all over again if that happens.
Neo Nazism and racism are a threat to our country.
Another reason why people hate the Antifa is because their portrayal. There's been fake Antifa accounts on sites such as Twitter. These fake accounts posted things such as Photoshop images of people being beaten senseless by Antifa members with texts saying things like "This person supported Trump, so he deserved it". This created a lot of negative attention towards the Antifa.
And there's also the media trying to cash in by scaring people with propaganda.
In other words, a lot of people hate the Antifa because they're just simply full of confusion and fear.