I'm not sure anything is really "natural" anymore. I'm sure that many of my stones are cut from a quarry with modern techniques. I can see tool marks clearly on my nagura.
You're not the first one to warn me about glue. And I believe that's a valid observation on many (any) boards.
I am very careful on just where I acquire my tools--both for my clients and for my personal use. I would draw your attention to the manner in which these Japanese boards "sucked up" the oil. Even if some sort of adhesive is used, it must be of the minimal nature. I buy only from Japan directly.
But consider this. Over the past year or so, look at the craze over the santuko knife. Not one in a hundred of these knives has ever seen The Land of the Rising Sun. Most are stamped steel. And if you bought one for $39.95 you can bet it's a knock-off.
(I've seen a Santuko made by Avalon, which I think is a German owned company that private labels. My point is that it is possible to own a Japanese designed knife, stamped out in China and owned by a corporation in Germany. Is this "natural"?)
But when I hand a knife like an Hattori over to someone who has never seen one, you ought to see their face!
So in selecting my ancillary tools, I use the same criteria--and it has paid back in some major results. Everytime I incorporate some truly Japanese tool or practice into my sharpening, my edges get better.
Now, you may not like or use bamboo boards. And I'm not trying to talk you into it. I would characterize my course of study here as more "raking sand." I enjoy the study, the experience, the calm joy, the resulting fulfilment.
In the final analysis, did you ever dine traditionally by sitting on the floor in an Asian restaurant? Did you ever eat with chop-sticks? Ever see any Japanese cinema of stories in their history, and filmed by their directors? Quite an insight.
This is my side of the debate, simply. Just another view.