Printable automatic weapons? DIY genome editing? We've come to a point in our evolution as a species where it's not possible to limit the "things" people can obtain. What's more important is creating a world where people have no reason to do harm. "Well there's no way to guarantee that". Sure. But we allow corporations to draft zoning laws so that people have to drive further to work and so that public transportation remains a failure in most cities. We also allow gross wealth inequity. We try to con mothers into abandoning breast feeding (yes, this still happens, I witnessed it a couple weeks ago), and when that doesn't work we make it as difficult as possible for families to spend time with their kids.