Don't all the helmet ideas also apply to wearing a helmet while doing any activity?

Don't they apply even moreso to gentler activities? A lower-energy impact is more easily protected by a helmet than a high-energy. That's why bike helmets are rated for a 6 ft drop and not for car-energy type impacts. ...Tho they would seem likely to reduce the injury of any impact.

Anyway, the sort of head injury resulting from a fall while walking or running would compare very well to the ideal scenario for protection with a helmet. Also, many, many peds and runners are hit by cars -- likely moreso than are hit by cars while biking.

Especially when out and about in slippery conditions a helmet would offer protection while doing anything.

My question is why is cycling highlighted for attention by those who want to wear rigid plastic on their heads?

Is there a particular hazard threshold constant that all cycling exceeds? I don't think so. There's not even a ballpark figure. The risks of ALL cycling aren't remotely close together.

For sheer numbers of head-wacks, car-driving has to be up there. Helmet wearing would surely reduce injuries there.

Bathroom slip'n'fall head injuries are enormous in quantity. Just hang a helmet on a hook by the bathroom door.

Driving, bathrooms, walking/running: these are the sources of nearly all head injuries. Right?

Really, a helmet might help reduce a head injury at ANY TIME doing ANYTHING so why not wear one ALL THE TIME? Better safe than sorry, right?

Why worry about the odds? If everyone wore helmets all the time we would surely prevent many thousands of injuries annually and save billions. Who cares what the activity is. The "better safe than sorry" logic shouldn't be used with an activity bias. I mean, let each sport decide for itself and each person. But in general if you want to save money and reduce injury, encourage everyone to wear one at all times.