An enjoyable ride but very slow ride indeed. Sheet ice everywhere. One of the best safety features a cyclist can have is judgement and mine was poor in this instance. Walking down the verge on a steep, thick ice covered, descent was certainly enough to remind me that cycling safety starts with the noggin.
Now that i mention the noggin.....
Cycling is in no way comparable to walking or driving a car. It is probably closest to riding a moped or low powered bike. Both of which a helmet is a requirement, though this is a little off topic. I assume you are going to say something like "why don't people wear helmets whilst walking or driving a car?"
I would suggest we could debate that all day. Even if i think the answers are bleedin obvious, you may not. For this reason i ask you not to pursue this point and accept a cycling related answer. This is by definition a forum about cycling.
Cyclists can choose not to wear elbow pads, knee pads, safety glasses, body armour, steel toe caps, kevlar body suits or even a cup for the nether regions (you never know when you might need one!). The difference between all of these methods of self protection and a helmet is quite simple, the helmet is the only one that (arguably) protects your head.
You can break bones, drag your skin along gravel infused roads, snap ligaments and even land on the bars in a position you never ever want to land on the bars! Thing is you will walk away from these unfortunate incidents, you might not walk away from a serious head injury.
I bet a head injury whilst cycling is far more likely than winning the national lottery. I also would like to bet that there are plenty of cyclists (even on this forum) who play the lottery every week but don't wear a helmet. Think about it.......