My personal consistent principle? I would say, "1) According to the manner in which the product is advertised for use, and/or 2) According to the manner in which the product is actually used. When applying the above, I take into consideration the scope (if any) of the legitimate use of the product. Remember the McDonalds plastic coffee stirrers that had a little spoon at the end? Turns out that the spoon was exactly .1 cc, the ideal heroin dose. That met my #1, but failed #2. Okay. So for a dual-use product that is used by some for legitimate purposes, and by some for illegitimate purposes, what do you do? Do you ban it for everyone? Do you ban it for only the people who are using it illegitimately? If the latter, how do you enforce this?
"So for a dual-use product that is used by some for legitimate purposes, and by some for illegitimate purposes""Some" is what, a few? Less than "many", certainly not "most".
I'd say keep it legal.
But we usually have either most-legal, some- illegal (PVC pipe than can be used to make bongs) or some-legal, most-illegal (Tommy Chong's bongs).
Can you give me an example of a dual-use product that is some-legal, some-illegal?