Not really. For one thing, you assume that everyone is wearing their helmet correctly and has the right size.
Secondly, if the person does not have any major ill effects from coming into contact with the pavement or lamp post etc while wearing a helmet then it's highly unlikely that he will have suffered much injury to being with. It's pretty slim odds that you'll land on your head in the first place. Also, most helmets don't protect against neck injury. It's highly unlikely and improbably that your life will be saved by wearing one. However, just for the sake of argument, say it is spared, you'll be paralyzed. That's not any kind of life.
Thirdly, except maybe when it comes to children, helmets in general don't offer you much protection. Helmets themselves have limited utility, being useful only for preventing minor abrasions to the head. In other countries and in the usa, where there are bicycle helmet laws, the laws usually apply to children only not adults. People are already pissed off because they're reluctant to ride a bike worrying that they're going get fined for not wearing a helmet. Thus ridership will decline.
Fourthly, an hour of bicycling causes fewer serious head injuries than an hour of walking. Think bicycling is dangerous? Try the safety quiz at the Bicycling Life website. Think helmet laws work? Visit the “cyclehelmets” website.
Finally, to further add insult, to avoid getting a ticket by VPD for not wearing a helmet, all you have to do is to have it on your head, barely strapped on. Now, doesn't that, in theory, defeat the purpose of the law?