Simple helmet effectiveness test :
Take your head and drag it along the road at 15mph, press it into a belt sander, or run at a wall head first. Do this with a helmet and then without, and compare and contrast the damage to your head between having the helmet or not. Pretty conclusive hey? Hope you still have some scalp left.
I don’t think anyone has the right to tell a third party not to wear a helmet unless they have experienced themselves and can show proof of why you shouldn’t.
Statistics about effectiveness of helmets at 30mph or whatever are tiresome, how often do you go that fast. Personally when I had a cycle computer my average speed was something like 9 – 10 mph where I rode, I would say I very rarely reach 30mph, I don’t even know if my gears allow me to pedal that fast.