As a runner, I always run opposite traffic so I can see what's coming. As you said, being hit by a car with a few miles per hour less impact won't make much difference. I usually run on roads, except when I'm on a busy boulevard.
I don't think bicycles have that choice. They're not allowed on sidewalks with pedestrians, so they have to conform to the same rules of the road as cars.
I've been an avid cyclist for a LONG time, since the days of Greg Lemond. I would never, ever ride against traffic, no cyclists I've ever ridden with do that. There are several reasons apart from what you mention. As others have also said, the closing velocity is much greater- on a flat road I may be doing 20+ mph, a car coming toward me is probably doing 30+ mph. That's less time to react (remember, there are blind curves and hills that create blind spots) and of course a much more violent collision.
Also, and some otherwise cool-headed people might get triggered by this, but many cyclists ride in groups. I used to do weekend rides in a group of 20+ cyclists. Under no circumstances do you want a group of cyclists riding
into traffic.
I can usually hear cars behind me in plenty of time to move over, assuming there is somewhere other than grass and dirt to move over
to. You can now get lights for the back of your bike that also have radar and will pair with your bike computer so you can see cars approaching from behind. But the reality is, where there are no decent shoulders it's dangerous. I don't feel as indestructible as I did in my 20s and 30s and nowadays I do most of my riding virtually, indoors. Safer and I don't have to worry about fixing a flat tire 20 miles from home.
