Sorry but helmets do help whatever the speed. I think the issue is the statement "helmets save lives". This is probably not true. Yes in certain instances a helmet will not save your life. However a helmet will reduce your chance of a head injury.

As a person who has had two high speed crashes in which my helmet took the impact and a friend of a person who has a serious head injury which has really impacted his entire life (he still has head aches, cannot be in crowded rooms, depression etc), please wear a helmet. And one that fits properly.

Most visors unclip off the helmet so you don't have to have them if you don't want them.