Personally I wear protective clothing when I ride - I know that it is only good to a certain point, and will not help me in all situations.
I shake my head at those that don't but I do not tell them what they should or should not wear as it is a personal choice. As long as they understand the risk they are taking and are willing to suffer the consequences if they were unfortunate to get into an accident (and I hope they don't) well that is their choice.

