The issue is that historically the authoritarian leftists (marxist-leninist groups) turn on every other leftist group the minute they gain power, rounding up anarchists or regular Marxists to either imprison or execute them.
It has happened very consistently, such as during the Russian Revolution, Chinese Revolution, Spanish Civil War, etc. Without that historical context it makes it seem like the infighting is over pointless squabbles, when in actuality it's Anarchists and Marxists trying to prevent people from being tricked into supporting an ideology that would result in yet another lethal purge and dictatorship were they to gain traction and political power.
Which, ya know, I think is a pretty reasonable concern.
