Going back to the OP, the question is about normalisation of helmet wearing. And I think it's an interesting one.
Normalisation being that helmet wearing is now pretty much the default position. Your Uncle Fred, who hasn't ridden a bike since 1979, will notice and comment if you're not wearing one; Your cousin Jane, who hasn't ridden a bike since 2007 and has decided to buy one will assume a helmet to be a necessary accessory, possibly even a legal requirement, just like brakes. Kids wear helmets from the age of dot upwards.
As mentioned above people tend not to do their own a personal specific risk assessment for cycling, they just take the an off-the-shelf one from popular culture, and that off-the-shelf risk assessment mandates helmets.
Is the specific requirement for helmets in this popular culture assessment suppressing take-up of cycling?
I think the basic answer is we don't know and we can't know, but we can pontificate and formulate reasonable but totally untestable ideas suggesting that it does or doesn't discourage would-be cyclists. (See above)
We are where we are. Helmet wearing is normalised. If you could get a message across, which would be better? A general message that cycling is not as dangerous as you think? Or a specific message that cycling is not dangerous enough to warrant wearing a helmet?
The reason I ask this is that I wonder if we sometimes get too hung up on the specifics of helmets, and high vis, or this or that equipment and lose sight of the bigger picture which is excess fear of cycling.
And let's face it, cycling in traffic can be frightening, whatever the stats say. At least, I find it to be so, and I've done a lot of it. Bear in mind that behind this faulty risk assessment is genuine fear. And fear is an emotion that isn't really going to be affected by clever infographics or deaths-per-mile-travelled* stats. It's all very well to condescendingly point out how bad people are at risk assessment, but unless a way is found to address the underlying fear then just telling people that they are being a bit stupid and should up their risk assessment game will only make matters worse.
* A completely unhelpful measure.