I think you're both focusing on remote edge cases when much more obvious, frequent, and unfeasible snags will arise.
In cities, the only thing keeping pedestrians patiently waiting on sidewalks (instead of trying to cross streets in front of cars) is their uncertainty re: the attention, competence, and sobriety of approaching driver. If cars dependably screech to a halt whenever you dangle a leg (or a baby carriage or an umbrella) in front of them, then every pedestrian becomes an invincible King of Traffic, and every urban area becomes irresolvably choked. Unless you put a cop on every single corner, you won't mitigate via enforcement.
It's fatal. Traffic nerds concede it won't work unless we elevate urban traffic above current street levels.