This post in /r/science links to an article whose findings are summarised by OP as: 'Effects of Bicycle Helmet Laws on Children's Injuries: "helmet laws are associated with reductions in bicycle-related head injuries among children. […] the observed reduction in bicycle-related head injuries may be due to reductions in bicycle riding induced by the laws'.

/r/science immediately responds with their favourite tactic... the personal anecdote.

Top comment, completely unsupported by evidence:

In Germany, there is no law mandating helmet use for bicyclist of any age. They cite an over-all greater benefit to the population's health from bicycling without helmets since more people bike. (Helmet-hair is the main culprit) ( 104/-14) link

High level comment, sitting at 40 when I saw it:

I don't really care about helmet hair, but I don't like wearing helmets because they're bulky, hot, heavy, and restrict head movement / visibility. It takes the 'fun' out of biking. Plus there's no good way of dealing with the helmet when you get to your destination. You can't roll it up and put it in your pocket, or leave it with the bike. You have to carry it around and it's another thing to worry about. I mean, all of this sounds like a minor inconvenience, and it is, but I was on the fence about biking anyway. This just gives me a reason not to. On the other hand, I hear stories from time to time about someone who fell down and left a huge gash in his helmet. I wonder if that huge gash would be in his head if not for the helmet. It's hard to say for sure because the physics change a lot with a helmet. Your head is bigger, heavier, and made of a different material with a helmet. It might also change the psychology of falling (I need to protect my head less and my elbows more...), plus helmets are designed to break after they hit something. link

Then there's just highly upvoted anecdote after anecdote after anecdote. At some point it changes into a discussion on the merits of helmets for skiing, but that's still full of anecdotes rather than actual analysis.

Below the anecdata, the thread devolves into a discussion of how the mean old government tells people how to take care of their bodies -- wearing seatbelts, wearing helmets, it's all the same.

I agree. I'm getting tired of the government telling me what I can and can't do with my own body. I know the risks. If I want to risk my life on a bike, there shouldn't be a law stopping me. I'm not hurting anyone else by not wearing a helmet. Just leave me the fuck alone. ( 21/-7) link

But what about reddit's greatest fear, people who don't take care of themselves and wind up becoming a drain on the health care system?

Depending on your injury, you are affecting people other than yourself. What about if you fall and suffer head trauma to the point you are now in a vegetative state? Now you are a drain on the hospital system and the taxpayer system because you decided to not wear a helmet. ( 11/-4) link

And...

I'm with you...except that injured uninsured cyclists impose a burden on society. Also, we don't hold kids responsible for their actions. They're kids. I'm pretty ok with saying to adults: "You skipped the helmet AND you're uninsured? You are an organ donor." "b-b-b-b-b-b-u-t it's just a little road rash!" ( 11/-3) link

And since we're so far off topic already:

uninsured fat people are also a burden on society. ( 4/-1) link

Someone attempts some analysis of the story with a little bit of "the kids these days":

I wouldn't say children aren't riding bikes because of the helmet laws. They aren't riding bikes because we're all just getting lazy. ( 16/-4) link

The rest of the thread, with very few exceptions, is composed of lower ranked anecdotes. Dozens of them, some as simple as this:

When I grew up no one wore helmets. I never saw or heard of a single head injury. ( 2/-0) link

It's an egregious thread because it completely fails to engage with the source material, but also because several jerks within combine into one completely useless megajerk:

• In my country we do it this way, in your country you are wrong

• Anecdata being presented and upvoted as if it is completely relevant. Getting off topic is totally fine, because it means there's more anecdotes to be shared!

• People who make any kind of choice that I don't agree with are burdening me with their medical costs.

• Why won't the government just let me be free?

• Kids these days are lazy and useless.