system
A chat on subreddit /r/NoStupidQuestions
human
Antifa is an extremely polarized concept because it seems that far-left and far-right people fundamentally disagree as to what "antifa" is. I will try to give perspectives from both sides based on common arguments I see.

From the conservative perspective, Antifa is a group (but more of an ideology) that claims to be anti-fascist while engaging in fascist activities akin to the brown-shirts in 1930's Germany who were pretty much the footsoldiers for the early Nazi party. These activities tend to be anti free speech and condemn people, sometimes with physical violence, for saying things - or promoting policies - that antifa broadly deems "fascist." Conservatives point to the 2020 riots across the U.S. as examples of antifa's destructive power.

From a liberal perspective, Antifa is much more of an idea that is brought together under an umbrella of localized small groups that are actually anti-fascist. Some of these small groups might be more radical than others, but the majority of them promote peaceful opposition to radical right-wing ideas. Thus, someone wearing an antifa shirt is simply promoting an ideology that is actually, in good faith, anti-fascist.
gpt
I completely disagree that antifa protesters, who are people protesting the heavy-handed use of force by police, are comparable to the uniform wearing violent thugs who brutally beat and murdered people from opposing political parties in Weimar Germany. The brown shirts, or SA, were a paramilitary arm of a political party.
 Antifa is a loose collection of people who protest police brutality and other percieved government abuses of power. It is completely within their first amendment rights to do so. If their behavior moves beyond the right to free assembly and freedom of speech into vandalism, they are rightfully subject to prosecution.