The idea that blowing down the barrel is inherently unsafe is only applicable in the context of centerfire weapons with some sort of magazine.
With the exception of double barreled weapons, 99.999% of the readily available for purchase muzzleloading rifles, pistols, and smoothbores contain only a single shot. They have no magazine of any sort where another powder charge & projectile could possibly lay in wait to be inadvertently loaded into the barrel. In addition, all currently available muzzleloading weapons available for purchase, require priming the pan of a flintlock, placing a percussion cap on a nipple, or in the case of most inline rifles, placing a #209 shotshell primer into the cavity of an inline breech plug. As a result of this fact, it is nearly impossible to shoot oneself in the head by blowing down the barrel of an already fired, unloaded weapon.
Does blowing down the barrel look dangerous, especially to those unfamiliar with muzzleloaders in specific, and firearms in general? Of course.
Over the past 20 years, or so, it has been far easier for the muzzleloading community, at the behest of the NRA in particular, to capitulate to the naysayers, the lawyers, and those members of our society that sue both companies, & individuals, for profit. As a result, very few ranges are able to obtain insurance against possible liability unless they adhere to the stipulations that the insurance companies lay down.
In our current anti-firearms society, no insurance company will issue a policy if there is the least possibility that any behavior at a shooting range is considered to be dangerous. This is even more true if something looks dangerous, even if hundreds of years of practice has proven it to be safe. Like blowing down the barrel.
In my lifetime I am not aware of any person being injured, or killed, as a result of blowing down the barrel of an already fired, empty, single-shot, muzzleloading rifle, pistol, or smoothbore.
Every injury, or fatality, that involved a muzzleloading weapon of any description, from real cannon, to hand cannon, to matchlock, to wheelock, to snaphaunce, to migeulete, to flintlock, to sidelock percussion, to inline percussion, that I have ever read an account of, or had told to me by another person, was a direct result of the loading process, the priming process, or the act of shooting.
And each, and every one of those incidents (several dozen that I am aware of) was the direct result of carelessness, ignorance, inattentiveness, hubris, stupidity, idiocy, or outright insanity on the part of the shooter.
Instead of mounting a high-powered advertising campaign when the first inklings of criticism were leveled against blowing down the barrel, the muzzleloading community in general chose to capitulate.
In the centerfire world of firearms there is no legitimate reason for placing the muzzle of any weapon near one's head/mouth, unless the person is hell bent on suicide.
The same is not true for muzzleloading, but the time to take any kind of stand that could possibly make any kind of difference as regards to blowing down the barrel is long gone.
As long as any muzzleloading forum will allow me to exercise my 1st Ammendment right to Freedom of Speech, I will stand up and defend any muzzleloader's right to blow down the barrel. It is a personal choice, just like choosing to wear a helmet when riding a bicycle, or motorcycle is.
Like I said in my above post, you can't legislate competence, intelligence, attentiveness, or common sense. Which, in my lifetime, I have found to be not at all common.