Depending on how/where you ride, a helmet can be anything from "useful protection" to "cool looking ornament". Let's face it, in a direct hit to the head at 25 mph a bike helmet will do very little.

Skiers also have these arguments all the time. Skiers helmets are more robust, yet direct impacts at high speeds can be fatal just the same.

I don't wear a ski helmet, but I do wear a bike helmet. The bike helmet is there for protection against minor accidents. Anything beyond that is a risk I have to manage and take responsibility for.