The question to be asked here surely has to be:

a) am i in danger of getting an injury to my head much more when riding a bike, than at other ordinary everyday actions,
and
b) if a) is true, is a bike helmet giving me significant better odds?

For a) i don't really think so. We do lots of stuff every day about as "dangerous" as cycling without even wasting a thought about wearing special protective gear. And this would make discussing b) kinda futile in the first place.
But simply by looking at the construction of a bike helmet and comparing it to other helmet types (motorcycle, climbing, construction work etc.) it should be clear that bike helmets have very narrow limits of how much additional protection they can provide.

Of course, one can say "i don't care about this, *in case* i fall and hit the pavement/the car/whatever with the correct spot, its better to have 2cm styrofoam in between than nothing" - and that is absolutely ok.

What i don't like about all those helmet campaigns and advocacy are two points:

1) they make cycling look more dangerous than it really is
and
2) they put an undeserved emphasis on the importance of passive protection gear at the expense of the thousands of other factors which decide whether you make it home from a ride in one piece or not. And some of these have way, way more influence on that than what your preferred headgear is. Like, most importantly HOW you ride.

Cycling safety neither starts nor ends with a helmet. In fact, its far from it. If you want to wear one, absolutely fine with me. I just wish people would stop putting "safety" (or "common sense") equal to "wearing a helmet".

Simple rules:
What you would't do without a helmet, don't do while wearing one
Ride as if you wore an invisibility cloak
Ride as if you had 100 bright red blinkies on you and the first car driver to run you over was awarded 1 Mio $

and you have a good chance to survive (which isn't all that hard).