> It seems a lot more reasonable to prosecute kidnappers rather than the makers of generic tools.

As someone who is pro 2nd-Amendment (but not pro-gun) I of course appreciate this argument.

There are certainly gray areas. The most immediate example that comes to mind are bongs or other items used for smoking pot (maybe other things? I'm not too sure). Ultimately it comes down to what the government and regulators think, what they can argue in court, and so forth. And if the people don't like it, they can take democratic political action.