Unicycles are actually very safe.
Since the pedals are fixed to the wheel, there is no free spinning.
Either the rider is above it and in control, or they are on their ass and the uni next to them.
Unis are small, slow and safe.
As a teenager I would go out for a ride, put it on my shoulder for hikes and then ride it back by bus.
So when you take the novelty off (and as a rider, it vanishes quickly) it's just a very fun and convenient bike
It's hard to use a unicycle brake as a true panic brake. It's essentially an ejection seat if you abruptly press a brake too hard.
But they are useful as drag brakes! I run a disc brake on my mountain unicycle, and really it's to make super-steep downhill segments feasible (at least without requiring a tremendous amount of back pedal pressure). I choose a brake used for trials biking with a long throw range.
I have a rim brake on my 36" unicycle. In that case it is helpful to reduce stopping distance, in part because the crank-to-wheel ratio is bonkers, but it's still primarily used as a drag brake on long downhills.
But yeah, on a mountain/street unicycle, your feet aren't that far off the ground, and you can't really go faster than sprinting speed. The big risk is getting tangled up in a weird way on the mountain.
36" distance unicycles can go faster than sprinting speed. Bailing unexpectedly on a fast 36" results in a few galloping steps and hopefully not a trip and slide...
Fun little unicycling factoid: "UPD" stands for Unplanned Dismount, and really is what tends to happen more than actual crashes. You realize your balance envelope is blown and there's no hope of making the line you're trying to hit, so might as well just dismount gracefully while you still can.
Indeeed, I feel there's a defense mechanism in there about the implicit menace in someone doing something beyond your own ability.
Unycicling is easy to put down, but take the message above about running barefoot.
Seeing someone doing something unusual like that, something that people "just don't understand" leads to uncertainty. "Why I don't do that?", "Why I can't do that?"
And since as men we're culturally primed to rubuff such doubts, the response is ridicule: "Because he looks silly, and I'm smarter than him", "Bet he'll get scared if I stomp", etc.
I used to unycicle around when I was about 16YO. I didn't get much response, really, maybe because my age made it less ridiculous or maybe intimidating. Still, I got a lot of free drinks and requests for trying when bringing it to music festivals
I've been using Dimio's Speech for a decade now, but it seems silly now that much better voices exist.