It’s insane to me how the fuckcars movement went from “we should have walkable cities and more public transport” to “ban all cars”.

have you read the sidebar of the fuckcars communities?

From Wiki (emphasis mine):

The car-free movement is a broad, informal, emergent network of individuals and organizations, including social activists, urban planners, transportation engineers, environmentalists and others, brought together by a shared belief that large and/or high-speed motorized vehicles (cars, trucks, tractor units, motorcycles, etc.)[1] are too dominant in most modern cities. The goal of the movement is to create places where motorized vehicle use is greatly reduced or eliminated, by converting road and parking space to other public uses and rebuilding compact urban environments where most destinations are within easy reach by other means, including walking, cycling, public transport, personal transporters, and mobility as a service.

From Reddit (emphasis mine):

Discussion about the harmful effects of car dominance on communities, environment, safety, and public health. Aspiration towards more sustainable and effective alternatives like mass transit and improved pedestrian and cycling infrastructure.

From lemmy (emphasis mine):

An place to discuss problems of car centric infrastructure or how it hurts us all. Let’s explore the bad world of Cars!

Equating the fuckcars movement to "ban all cars" is like equating climate change to "ban all oil".

Not to mention that they fully expect people to go grocery shopping every single day, or it never crosses their mind because they have no idea what it takes to feed a large family.

My aunt feeds a family of five. She does not own a car, nor does she do grocery shopping every day. You know what's the answer? You had it right - “we should have walkable cities and more public transport”.