But it doesn't change the truth of the sentence: "The exercise benefits of biking do way more to increase your life expectancy than skipping a helmet does to reduce it."
They're uncomfortable, mess up your hair, make you extra sweaty, and you need to put them somewhere.
None of these are good enough reasons to not wear a helmet while you're riding a bike, but any one of them would be a good enough reason to not ride your bike at all. That's the point OP is trying to make by saying you can skip your helmet if you want.
If that comparison was apt, we wouldn't see so many people out riding sans protection.
But we do, and it's because they have a share bike that didn't come with a helmet, or they were worried about messing up their hair, or they lost their helmet, or they left it at the destination, or they're a rebellious teenager who just doesn't care, or no-one educated them about the risks, or they just forgot to put it on.
A better comparison would be to flossing your teeth, or wearing sunscreen: everyone should do it, but not everyone will do it.
There is ZERO reason not to wear a helmet every time you leave the house. You could trip and fall at any moment!
Presumably, you're willing to accept that risk. Biking without a helmet is no doubt riskier than walking without one, but both activities are well within reasonable risk-taking range.
You don't need me to tell you why I don't like wearing a helmet when I bike; you already use all those same reasons to avoid wearing one when you walk.
I'm sorry that you think my position is absurd, but I assure you it's offered in good faith. There are only trade-offs. This isn't just a comment on the wisdom of helmets; this is, as far as I can tell, an actual feature of the universe we inhabit. There aren't "problems" and "solutions to problems"; there are only trade-offs.
I (honestly and in good faith) place walking and biking in the same "helmet not required" risk category. The point isn't whether or not you adjust the risk slider further in one direction than me. The point is to respond to the assertion that there is zero reason to avoid wearing a helmet. We all know that isn't true, or we'd all wear helmets all the way down the risk scale.
Where you place "time to put on a helmet" on the scale isn't really the point. The point is that the scale obviously exists and it's obviously the case that there are places on the scale where not wearing a helmet makes sense, because if it were literally the case that there were no tradeoffs, then there'd literally be no reason not to wear one at all times.
That's the reductio proof I'm trying to illustrate.