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
Also depending on who you talk to the 2020 riots were protests. Not riots. 

Both sides like to do false flag accusations as well. Which has been proven in a few cases. Like cops or proud boys dressing in all black to look like antifa, getting property damage started and riled up, then saying “look at the rioters” when it would have otherwise been a largely peaceful affair. 

There are also opportunists who you can’t fairly assign to either “side”. They take advantage of the goings ons to smash/grab and do chaos. The right likes to associate these people with the movements they operate around, but it’s disingenuous