I,m not forcing people to wear helmets, - I think you should - but the most likely culprits will be insurance companies when personnel liability insurance takes off in this country (which they way its going it's not far away)
Already all this safety stuff on building sites is more to do with liability insurance than actual protection.
do you really think a little yellow helmets going to help when someone drops a 10 ton girder on you.
It does help in the same way a cycle helmet helps, to a limited degree in limited circumstances.
but there is plenty of studies that show the benefits of helmets, - it's up to you whether you read them or not.