It may appear that it's middle aged men who are the most vocal (they tend to be about just about any topic), but when Australua brought in MHLs, the demographic with the greatest fall in cycling rates was teenage girls.Just an observation and not research but it seems to me that the anti helmet thing seem to be an obsession of the white middle aged, middle class male road cyclists. Outside this group I find the attitude to helmet wearing to vastly different. The working class commuters who don't wear one mostly would if became mandatory in the same way they did after mandatory seat belts etc. The active MTBers wear one as it's deemed an sensible thing to do when riding techy trails and its use other places is normalised.
Being vocal and having behaviour affected are not necessarily linked.