I hope this doesn't break the debating rules and whatnot xD I do like to get into the meat of a conversation (used to competitively debate, you see), and in advance just let me say that I am neither offended nor intending to offend. I know you can't be too careful online, where tone doesn't really carry across!
What I mean to say is that personal freedom is only a direct reason to not wear a helmet only if you're saying, "I have the right to not wear a helmet, therefore I choose not to just so that I can exercise that right." Personal freedom isn't the direct reason if you're saying, "I don't want to for reasons x y and z, and luckily for me I don't have to wear it, so I can listen to my reasons and not wear a helmet. Hurrah!" That's the kind of distinction I was thinking of. In the latter case, your real reasons for not wearing a helmet are x, y and z. And obviously x, y and z are all good reasons for you to make that decision, or else you'd be doing things differently.
And if you told me to mind my own business, I wouldn't argue back xD The only people I'd force helmets onto are close friends and family, because, you know, they're mine so they don't have the right to do things I think are silly :P I study chemical engineering, and we do work on pilot rigs (small-scale chemical plants, e.g. A distillation column 7m high instead of 70m) with lots of safety rules. For example, you should always have three points of contact on a ladder. So my classmates and I pointedly count how many hands and feet are touching when we go up and down them and tell each other off if they're standing there with one foot and one hand in the air xD And if someone takes off their safety hat or goggles, someone else will ram them back onto their head for them.
But the pilot rigs are a bit different xD Not wearing a helmet when riding is a personal choice, whereas we've all signed bits of paper saying we'll obey lab rules, and we also don't want to fail labs for not following proper safety procedures!
I'm not attacking the views of those who don't wear helmets, even if I have reasonably strong feelings in the other direction. I'm just indulging my liking for an engaged discussion and curiosity about different practices. Hope that's okay :)
If you believe everything you read, better not read.