Jan Gehl, architect of Melbourne's livability revival over the last 20 years, speaking in Melbourne on the above date, (watch on Youtube, quote is from 1 hour 31minutes) "I think that you should reconsider your mandatory bicycle helmet. We have figured out, that if mandatory bicycle helmets were introduced in Denmark we could cut to half the bicyclsts over the night, we are urging people to use bicycle helmet but we know there are a number of situations where you can't get hold of one, or you have been to the hairdresser or you are going on a date or I don't know what and it has been found out that it is much cheaper to have many people bicycling than to reduce the number of brain injuries for small little group of fanatics who bicycle in the young age, so it is good economy if people bicycle and be a little bit more lenient about their protection... So I think it would be fantastic if Australia took this little step to say you can decide yourself but you are very clever to use your helmet." and in response to the Australian presenter saying the roads need to be safer: "The more people who bike the safer it is".
In the UK, Kevin Hickman wrote: (emphasis added)
I view helmets, and hi-viz, as just an indicator of how safe people feel. If
we get the everyday environment people are cycling in right then the personal
protective equipment will vanish.
The truth will out eventually, and
either we'll all be putting helmets on as our heads leave the pillow in the
morning, or they'll just fade away, or people will continue to use them where
they feel exposed to risk.
I agree that helmets aren't helping the
normalising of cycling, but it can probably be sidestepped by getting the
environment right, and thankfully that's where the focus is shifting to now.
And let's not forget, helmets are such a phaff that if we do get the masses
cycling they're not going to bother taking helmets with them everywhere.
And conversely, if people still feel helmets are necessary, the
masses won't cycle.
Apart from the issue of compulsion, which where it
occurs appears to mean 'game over' for mass cycling until it's repealed,
helmets are
just a distraction.
Here'sa graph of pedestrian and bike fatalities, with the pedestrian figures scaled to have the same average. There is more noise in the bike figures because the numbers are lower. The drop in fatalities around the time of helmet mandation is often cited as evidence for their effectiveness, note however that the drop in pedestrian fatalities is very similar, indicating that helmets were not the reason - other road safety factors introduced at that time must have been the most important cause.
In country towns the decrease in cycling after helmet laws is even more pronounced than in capital cities, perhaps because increasing congestion acts as an incentive to cycling, masking the depressing effect of helmet laws.
Join the Facebook group Freestyle Cyclists to organise against helmet laws.
Debate on The Conversation, here's a contribution from Dorothy Robinson, UNSW:
The new analysis doesn’t show that helmet laws reduce head injuries, only that there might be some small benefit in the event of a crash.
Unfortunately, there is very strong evidence that helmet laws increase the likelihood of crashing, because of risk compensation and reduced safety in numbers. Table 2 of the paper “Head injuries and bicycle helmet laws” Accident Analysis and Prevention, V28, 463-75, 1996 shows that the risk of a child cyclist suffering a head injury increased by 27%, and the risk of a non-head injury increased by 72%.
The increased risk of crashing totally negates any possible benefit of helmet laws, and also discredits the methodology used in this study.
Within two years of the helmet law, there were 44% fewer children cycling in NSW, according to comprehensive surveys carried out at the same time of year at 120 sites (72 in Sydney and 48 in regional and rural areas) covering road intersections, primary and secondary schools and recreational areas.
Female cyclists were particularly discouraged by helmet laws. The risk of head injury varies with the age and sex of the cyclist, and also increases 3 to 5 fold for crashes involving motor vehicles. If helmet laws discouraged on-road cycling for transport more than off-road recreational cycling, the change in the proportion of head to arm and leg injuries would have changed simply because of the change in the type of crashes, irrespective of whether or not helmets provide significant protection.
One overseas study showed that people who don’t cycle to work had 39% higher mortality rates than those who cycled without helmets. Helmet laws have led to clear and significant harm from discouraging a healthy and environmentally form of transport, from reduced safety in numbers, and from risk compensation. A UK study showed that drivers leave more room when overtaking cyclists without helmets. The researcher, Dr Ian Walker, was hit twice when conducting this research - by a truck and a bus - both times when he was wearing a helmet! http://www.eurekalert.org/pub_releases/2006-09/uob-wah091106.php
Whether or not helmets provide a small benefit in the event of a crash is almost irrelevant, compared to the big effect of helmet laws in discouraging healthy activity and environmentally-friendly transport and increasing the risk of head injury because of risk compensation and reduced safety in numbers

"Even the most optimistic model requires about 11,000 helmet years to
prevent a head injury, with 90% of these being relatively minor (short
stay in hospital)" Dorothy L Robinson, UNSW
Latest news: yet another study shows that mandatory helmet laws do more harm than good, but Bike NSW fails to understand and so they undermine cycling just when hope is dawning: SMH article. See other media.
The paradox of mandatory helmet laws is that while there may or may not be a benefit to an individual rider from wearing a helmet, the effect of mandating helmets for all riders is unequivocally negative. Why are mandatory helmet laws bad public policy? Simply, they have a negative effect on public health outcomes. That's right, they don't improve public health: they make it worse. Seems illogical, how can this be?
First, understand the health benefits of cycling. It's estimated that the health benefits outweigh the risks by 20 to 11. Next note that Mandatory Helmet Laws reduced cycling in Australia by around 30% and continue to do so. So the health benefits lost because of helmet laws hugely outweigh any possible benefits from improved safety.
For example, research shows2 that cars pass closer to cyclists who are wearing helmets, i.e. cars leave more clearance if you aren't wearing a helmet. So wearing a helmet increases the risk of collisions.
There are plenty of papers examining the statistics, start with British Medical Journal article by Dorothy Robinson, UNSW, or cyclehelmets.org. 1Hillman, M., Cycling and the promotion of Health, Policy Studies, 1993, 14: p. 49-58 (thanks to Bicycle Promotion Fund for the reference)
2Research at the University of Bath: Wearing a helmet puts cyclists at risk, Walker, I. (2007). Drivers overtaking bicyclists: Objective data on the effects of riding position, helmet use, vehicle type and apparent gender. Accident Analysis and Prevention, 39, 417-425. Further remarks from this author