I’ve locked a helmet up with my bike all my life, in several different cities; It’s a complete non issue to me. What is the concern; that someone will use a blade to cut the helmet strap so that they can steal your broken helmet? It’s effortless to leave your helmet attached to your bike.
Edit - I’m not saying I support laws enforcing helmets for adults; I just don’t think that helmet theft is a big concern.
This really depends on which city you're in and where in the city you leave your bike+helmet.
I've had the ultra-cheap lights on my bike stolen. I've seen plenty of other bikes stripped of everything except the frame itself.
This is why I always take my helmet (and my lights) with me, lock my bike and the front wheel with a good lock, and chain lock my seat down for good measure. Haven't had anything stolen since -- even in some sketchy areas.
I agree with your presentation - the issue boils down to it not mattering how easy it is, it's the perception of how easy it is. Once people see they can leave their helmet with the bike and it won't get messed with or stolen then it can become normalised and the perception falls away. But the inhibition is in the perception that requiring a helmet makes it difficult.
Unrelated anecdote: the first time I went out with a helmet was the first time I banged my head, I ducked under a branch as I normally would, only I'd not allowed the extra room, banged my head hard and came off my bike (gently). I still wear and encourage helmet use.
