How do helmets change the argument?

Like seat belts, you can choose to wear or not wear a helmet independent of all other factors. The motorcycle or bicycle is exactly the same regardless of whether you're wearing a helmet. Also, everyone understands the benefits of a helmet. The benefits don't make everyone wear a helmet, but everyone is clear about why there are helmets.

It does, wearing helmets means you need to carry them around and store them, and it can ruin your hairstyle. People who can balance the tradeoffs make mostly reasonable decisions ("I write large programs with the support of a type system and eschew it for small scripts", "I will probably be OK without a helmet just biking slowly between two buildings at work") but some people will never accept the upsides as being worth it.

> some people will never accept the upsides as being worth it.

How is this any different from the selt belt case? "(1) believe they'll beat the statistics, and thus no statistical argument will convince them or (2) value their "freedom" a lot more than they value their own lives"

Would you really expect an article "The helmet is a biker's best friend" to convince them?

Everyone knows that a helmet helps prevent head injuries. That doesn't need to be explained. Whether the tradeoff of messing up your hair or whatever is worth it is up to the individual to decide, but there's nothing complex about the decision that needs an academic discussion.