Remember kids... always wear a helmet. (The almighty bikeradar helmet thread)

that it can be outweighed by seemingly trivial concerns such as comfort, convenience and vanity.

It's also about being the change that you want to see. Functional cycling isn't statistically very dangerous but it feels like it is. There are lots of things you can do to lower your risk before you put on a plastic hat and reinforce the general perception that you need to armour yourself just to pop down the shops on your bike.

It's also about being the change that you want to see

That would be a valid reason, although I'm not sure that it actually has any effect.

Have we had this yet? Is fastening a helmet to your bag annoying?

https://wearenewlane.com/

This Cycling Weekly article suggests helmets do not protect from concussion:

DO CYCLING HELMETS PREVENT CONCUSSION?

That whole paragraph would be an embarrassment to a reputable publication, but it's Cycling Weakly so no harm done.

"Concussion is caused by force, usually sudden deceleration acceleration, which may or may not be the result of a direct impact to the head. Therefore, a bike helmet cannot prevent mitigate concussion by reducing the acceleration...However, the primary role of a helmet is not to prevent concussion but to protect from structural skull injury to reduce acceleration"