It's a pressure point, over thinking this safety thing. My wife and I have actually gotten yelled at by other bikers because we'll often ride without helmets -- they apparently are offended, maybe moreso if we pass them.

But more than that, I often run on trails that I share (safely) with road bike riders, (thought they take 90% of the road - and you know who you are....). They are a grim faced bunched, doesn't look like many are having any fun at all. Runners nod and smile at each other, cyclists look like they are suffering someone's punishment.

Frankly, it seems to have gotten worse year to year.