Hostility towards anyone who owns a car is rather more rare from walkability proponents. Not totally unheard of, but hardly mainstream.
For example, r/fuckcars is massive. A large subreddit might not be considered mainstream, but it does have massive reach. A lot of people see this as one of their first exposures to car-free communities and do not feel welcomed by it.
I think it's somewhat of an optics issue, but it is very hard to find walkability communities online that aren't using terms like "car-brain". I know that these terms are targeted at a certain type of car owner, but without being familiar with the car-free community this is not always clear and can be a turn-off to car-owners who may be curious about learning more.
And maybe unavoidable: the US in particular is SO slanted towards absolute car dominance in most areas, that you end up with this sort of rhetorical whiplash just by favoring movement towards transportation balance. I've never heard the term "car brain" before you just said it, and yet I know exactly what you're talking about, and that for many people it will be entirely accurate.