Yes, it probably may do. But against that you have to weigh:
-Feeling safer and taking less care
I dont think that is the case,we are so open and vulnerable anyway,even if we wore a motorcycle helmet,it wouldnt make me feel any safer from other vehicles,and wouldnt encourage me to cycle any less carefully,i think i probably speak for the majority
-Appearing less vulnerable to drivers and therefore having them take less care around you
Again,this to me isnt the case,when im driving i dont check if the cyclist has a helmet on,so making it more likely ill get closer or squeeze em out.I give as much room as is poss all the time.
-(minor point in this country with its miserable climate) getting hot/sweaty and having this reduce concentration
If my concentration was affected by my temperature,id be in bed ill
-having the 'size' of your head increased so that in a few cases there is an impact whereas without a helmet nothing would have touched down
A possibility,
so you pays yer money etc etc