Note that the OP's rant is not about riding helmetless, but rather about people who ride helmetless while the helmet is hanging from their bars or otherwise strapped to their bike. Look, helmets might give some people a false sense of confidence, but there's no reason that they necessarily cause this. There's no reason in principle that someone wearing a helmet will have poorer or slower reflexes in a fall, or is more likely to fall in the first place, than someone who's not wearing a helmet. I ride both ways, usually depending on how far I'm riding and whether I'm going down a big hill where I'll be at high speed.
But the thread-starter wasn't talking about reasons to wear a helmet or not - he was talking about why the h*ll do people ride helmetless with their helmet strapped to their bike?

The one good reason for this I've seen offered is that people wear a helmet for longer riding but may still have it on their bike.

But I've also seen of people who never wear their helmet, but it's always on their bike. One professor in my department does this - the helmet is always strapped to his rack. Why? I don't know. I've never seen him wear it. Baffles me more than it pisses me off...