Helmets do not look silly! Well, maybe they do to everybody else, but when I see someone riding at any kind of speed without one I think "urk, crazy guy, better keep away from this lunatic".

Seriously. A helmet makes me think "oh, good, a real cyclist". Tight spandex in glorious multicolour can look a bit silly, and the prancing walk one gets in roadie shoes but helmets, no.