The proper question is "How dangerous is the rider?"
Over 4 decades of riding, including regular commuting in traffic, group rides, rec rides, LD rides and even a little racing, I've had maybe a dozen whoopsies, none of which required a trip to the doc or hospital...and I don't wear a helmet.
YMMV - point is that cycling isn't dangerous, but the rider might be.
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"Let us hope our weapons are never needed --but do not forget what the common people knew when they demanded the Bill of Rights: An armed citizenry is the first defense, the best defense, and the final defense against tyranny. If guns are outlawed, only the government will have guns. Only the police, the secret police, the military, the hired servants of our rulers. Only the government -- and a few outlaws. I intend to be among the outlaws" - Edward Abbey