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.