My #1 Blogson highlights a product he thinks is unsafe.
It's a booster seat for a motorcycle. I happen to agree with him, but for (slightly) different reasons. He highlights that the booster seat does not contain a belt for the child; I disagree with him on that point - you do NOT want something that anchors a rider to a motorcycle. I do agree that it's not the best idea, though - if the child does not safely fit on the back of your chosen motorcycle, odds are they're too young to safely ride.
Look at the picture. What's missing on that child? Footwear that properly protect the ankle, gloves, and proper pants. While I might make the decision to ride in only jeans and a tanktop (which is about 0.00001% of the time, and even then I'm wearing a vest), my kids wear full protective gear every single time. Now, granted, the booster seat has nothing to do with the other safety gear, but it leads into the larger issue.
One of Borepatch's commenters took him to task, equating his dislike of younger riders with taking one's younger children to the range. There's a lot of similarities between the two events, actually. Your kids have to have sufficient upper body strength to hold a firearm in a safe position before they can go to the range. They have to be able to retain a firearm under recoil. Most importantly, they have to be sufficiently mature enough that they follow your instructions, follow the four rules, and won't put themselves or others in dangerous situations if they get bored.
Just like on a motorcycle.
You might not think so, but even a small child who decides to wiggle back and forth on the back of a motorcycle can turn a leisurely ride into a moment of terror. BTDT - BabyGirl G. decided that she liked leaning into turns, and decided to "help" me around a corner. She waited until we were well into the turn, then leaned into it very fast, throwing the balance off in the corner. I felt her shifting her weight and was able to compensate without issue, but had I not been paying full attention it could have gotten unpleasant. And this is the action of a ~ 75 pound child on a 750 pound motorcycle with a 180 lb. parent present.
Kids should be of sufficient size that they "fit" the motorcycle - in my kids' case, they had to be able to touch the footboards of the Harley while their backs were touching the backrest before they could ride. This meant that they were anchored on the back of the bike and their feet would not be loose. This leads to one of the big problems I see with the booster seat - it makes an already unstable position (the passenger being higher than the rider) worse, as you put a small, most likely squirming little person way up high where every motion is going to be magnified.
This is not one size fits all, of course. Certainly there are plenty of kids who, at age 5, are plenty mature to ride on the back of a motorcycle. Conversely, there are plenty of teenagers who have no business being anywhere near two wheels, whether as rider or passenger. Much like there are kids that are perfectly safe and fine on a hot range at the same age - or unsafe at any age. It boils down, primarily, to knowing your child and being honest about assessing their maturity level in any activity with an element of danger.
For the record, something