Could you explain why you think that? That’s a pretty general statement. Are you imagining city biking here, or something more like racing in the country-side?
Some data about how this is dangerous could be convincing: https://youtu.be/Boi0XEm9-4E count the helmets.
Just to be clear, I’m not against helmets (I wear one, as is custom in my country).
Only if you are riding a bicycle completely unsuitable for commuting or general urban use; like a mountain bike or racing bicycle.
Commonly used bicycles in Denmark and the Netherlands look like this:
https://omidbikes.nl/wp-content/uploads/mat-zwart-7.jpg
Note the handlebars and upright rider position that basically prevent going over the handlebars during an emergency stop. That kind of accident just doesn't happen here.
Of course, even then, as a teenager I still managed to get myself into some interesting situations a couple of times. But never went over the handlebars :-P
I go back and forth about the helmet issue personally. Though I've almost never not worn one.
My general feeling is that it's not much of a burden to me. And while the cases where it's actually going to help are narrower than most people think (especially people looking from the perspective of a car impact), it does improve the outcome in those cases quite a bit. So it's worthwhile.
If nothing else helmets are good places to mount lights, which are definitely an important safety measure! :)