About a month ago, I posted about printable AR15 magazines. Now, Make reports that this has caused Thingiverse to reconsider allowing weapons and parts of weapons to exist on the site. More about it here.
I understand their concern - they want the site to remain accessible to schools, and schools will most likely block any website that shows how to create firearms. I don't think it's unreasonable to make those how-tos restricted by age.